
Qass 

Book— 



7-7. 



-Vl- 




STEAM ElSTGla^R-i^^ 



IN ITS VARIOUS APPLICATIONS TO 

MliXES, MILLS, STEAM NAVIGATION, RAILWAYS, 
AND AGRICULTURE. 



PRACTICAL INSTRUCTIONS 

FOE TUB 

MANTJFAOTUEE AND MANAGEMENT OF ENGINES OF EVEEY CLASS. 



JOHN BOURNE, C.E. 



irHW AND REVISED EDITION, 



NEW YORK: 
D. APPLETON AND COMPANY, 

649 & 551 BROADWAY. 

1876. 



«v^ 






\' 






1 



y 



^°'' 



d 



<^ RECEIVED ^< 



^/BRAH^ 



PEEFACE 



TO THE FOURTH EDITION. 



For some years past a new edition of this work has 

m called for, but I was unwilling to allow a new edir 

a to go forth with all the original faults of the work 

on its head, and I have been too much engaged in the 

ctical construction of steam ships and steam engines 

and time for the thorough revision which I knew the 

rk required. At length, however, I have sufficiently 

< engaged myself from these onerous pursuits to ac- 

ciplish this necessary revision ; and I now offer the 

vvork to the public, with the confidence that it wUl be 

found better deserving of the favorable acceptation 

and high praise it has already received. There are very 

few errors, either of fact or of inference, in the early 

editions, which I have had to correct ; but there are 

many omissions which I haye had to supply, and faults 

of arrangement and classification which I have had to 

rectify. I have also had to briag the information, which 



IV PREFACE TO THE FOURTH EDITION. 

the work professes to afford, up to the present time, so 
as to comprehend the latest hnprovements. 

For the sake of greater distinctness the work is now 
divided into chapters. Some of these chapters are alto- 
gether new, and the rest have received such extensive 
additions and improvements as to make the book almost 
a new one. One purpose of my emendations has been to 
render my remarks intelligible to a tyro, as well as in- 
structive to an advanced student. With this view, I 
have devoted the first chapter to a popular description 
of the Steam Engine — which all may understand who 
can understand anything — and in the subsequent grada- 
tions of progress I have been careful to set no object 
before the reader for the first time, of which the nature 
and functions are not simultaneously explained. The 
design I have proposed to myself, in the composition of 
this work, is to take a young lad who knows nothing of 
steam engines, and to lead him by easy advances up to 
the highest point of information I have myself attained ; 
and it has been a pleasing duty to me to smooth for 
others the path which I myself found so rugged, and to 
impart, for the general good of mankind, the secrets 
which others have guarded with so much jealousy. I 
believe I am the first author who has communicated that 
practical information respecting the steam engine, which 
persons proposing to follow the business of an engineer 
desire to possess. My business has, therefore, been the 
rough business of a pioneer ; and while hewing a road 



PKEFACE TO THE FOURTH EDITION. V 

through the trackless forest, along which all might here- 
after travel with ease, I had no time to attend to those 
minute graces of composition and petty perfection of 
arrangement and collocation, which are the attribute of 
the academic grove, or the literary parterre. I am, 
nevertheless, not insensible to the advantages of method 
and clear arrangement in any work professing to instruct 
mankind in the principles and practice of any art ; and 
many of the changes introduced into the present edition 
of this work are designed to render it less exceptionable 
in this respect. The woodcuts now introduced into the 
work for the first time will, I believe, much increase its 
interest and utility ; and upon the whole I am content 
to dismiss it into circulation, in the belief that those who 
peruse it attentively will obtain a more rapid and more 
practical acquaintance with the steam engine in its 
various applications, than they would be likely otherwise 
to acquire. 

I have only to add that I have prepared a sequel to 
the present work, in the shape of a Hand-Book of the 
Steam Engine, containing the whole of the rules given in 
the present work, illustrated by examples worked out at 
length, and also containing such useful tables and other 
data, as the engineer requires to refer to constantly in 
the course of his practice. This work may be bound up 
with the " Catechism," if desired, to which it is in fact 
a Key. 

I shall thankfully receive from engineers, either 



VI PREFACE TO THE FOURTH EDITION. 

abroad or at home, accounts of any engines or other 
machinery, with which they may become familiar in their 
several localities ; and I shall be happy, in my turn, to 
answer any inquiries on engineering subjects which fall 
within the compass of my information. If young engi- 
neers meet with any difficulty in their studies, I shall be 
happy to resolve it if I can ; and they may communicate 
with me upon any such point without hesitation, in what- 
ever quarter of the world they may happen to be. 

JOHN BOURNE. 

9 BiLLiTER Street, London, 
March Ist^ 1856. 



<^ RECEIVED ^< 



//BR AB>^ 



PKEFACE 



TO THE FIFTH EDITION. 



The last edition of the present work, consisting of 
3,500 copies, having been all sold off in about ten months, 
I now issue another edition, the demand for the work 
being still unabated. It affords, certainly, some pre- 
sumption that a work in some measure supplies an ascer- 
tained want, when, though addressing only a limited 
circle — discoursing only of technical questions, and with- 
out any accident to stimulate it into notoriety, — it attains 
so large a circulation as the present work has reached. 
Besides being reprinted in America, it has been translated 
into German, French, Dutch, and I believe, into some 
other languages, so that there is, perhaps, not too much 
vanity in the inference that it has been found ser- 
viceable to those perusing it. I can with truth say, that 
the hope of rendering some service to mankind, in my 
day and generation, has been my chief inducement in 



Vlll PREFACE TO THE FIFTH EDITION. 

writing it, and if this end is fulfilled, I have nothing 
further to desire. 

1 regret that circumstances have prevented me from 
yet issuing the " Hand-Book " which I have had for some 
time in preparation, and to which, in my Preface of the 
last year, I referred. I hope to have sufficient leisure 
shortly, to give that and some other of my literary de- 
signs the necessary attention. Whatever may have been 
the other impediments to a more prolific authorship, cer. 
tainly one of them has not been the coldness of the ap- 
probation with which my efibrts have been received, 
since my past performances seem to me to have met with 
an appreciation far exceeding their deserts. 

JOHN BOURNE. 

February 2d, 1857. 



■^'^ RECEIVED ^<f 




^/BRAR^' 



PUBLISHERS' NOTICE. 



In offering to the American public a reprint of a 
work on the Steam Engine so deservedly successful, and 
so long considered standard, the publishers have not 
thought it necessary that it should be an exact copy of 
the English edition; there were some details in which 
they thought it could be improved, and better adapted 
to the use of American engineers. On this account, 
the size of the page has been increased to a full 12mo, 
to admit of larger illustrations, which in the English 
edition are often on too small a scale ; and some of the 
illustrations themselves have been supplied by others 
equally applicable, more recent, and to us more familiar 
examples. The first part of Chapter XI, devoted in y 
the English edition to English portable and fixed agri- 
cultural engines, in this edition gives place entirely t<? 



illustrations from American practice, of steam engines as 
applied to different purposes, and of appliances and ma- 
cliines necessary to them. But with the exception of 
some of the illustrations and the description of them, 
and the correction of a few typographical errors, this 
edition is a faithful transcript of the latest English 
edition. 



CONTENTS. 



PAGE 

Classification of Engines 1 

Nature and uses of a Yacuum 3 

Velocity of falling Bodies and Momentum of moving Bodies G 

Central Forces 9 

Centres of Gravity, Gyration, and Oscillation 12 

The Pendulum and Governor 12 

The Mechanical Powers 17 

Friction 19 

Strength of materials and Strains subsisting in Machines , 25 

CHAP. I.— Genebal Description op the Steam Engine. 

The Boiler 34 

The Engine 46 

The Marine Engine 55 

Screw Engines Gl 

The Locomotive Engine 65 

CHAP. II.— Heat, Combustion, and Steam. 

Heat 71 

Combustion 73 

Steam 82 

CHAP. III.-r-ExpANSiON OF Steam and Action 05 the Valves 87 

CHAP. IV. — Modes op estimating the Powee and Performance op 
Engines and Boilers. 

Horses Power 102 

Duty of Engines and Boilers 108 

The Indicator 1J2 

Dynamometer, Gauges, and Cataract 116 

CHAP, v.— Proportions op Boilers. 

Heating and Fire Grate Surface 121 

Calorimeter and Vent 124 

Evaporative Power of Boilers 130 

Modern Marine and Locomotive Boilers 132 

The Blast in Locomotives 134 

Boiler Chimneys 133 

Steam Koom and Priming 140 

Strength of Boilers 145 

Boiler Explosions 149 

CHAP. VI.— Proportions op Engines. 

Steam Passages 154 

Air Pump, Condenser, and Hot and Cold Water Pumps 159 

Fly Wheel 165 



XII CONTENTS. 

PAGE 

Strengths of Land Engines 166 

Strengths of Marine and Locomotive Engines 171 

CHAP. Yll.— CONSTEUCTITE DETAILS OF BOILEKS. 

Land and Marine Boilers 177 

Incrustation and Corrosion of Boilers 1S8 

Locomotive Boilers 199 

CHAP. YIII.— CoNSTRucTivB Details op Engines. 

Pumping Engines 206 

Yarious forms of Marine Engines 214 

Cyhnders, Pistons, and Yalves 218 

Air Pump and Condenser 226 

Pumps, Cocks, and Pipes 233 

Details of the Screw and Screw Shaft 239 

Details of the Paddles and Paddle Shaft 241 

The Locomotive Engine 248 

CHAP. IX.— Steam Navigation. 

Eesistance of Yessels in "Water 270 

Experiments on the Eesistance of Yessels 273 

Influence of the size of Yessels upon their Speed 277 

Structure and Operation of Paddle Wheels 278 

Configuration and Action of the Screw 284 

Comparative Advantages of Paddle and Screw Yessels 288 

Comparative Advantages of different kinds of Screws 296 

Proportions of Screws 801 

Screw Yessels with full and auxiliary Power 303 

Screw and Paddles combined 305 

CHAP. X.— Examples op Engines op eecent Construction. 

Oscillating Paddle Engines 303 

Direct acting Screw Eng;ne 323 

Locomotive Engine • 333 

CHAP. XL— On various Forms and Applications of the Steam Engine. 

Governor 342 

Donkey Pumps 344 

Portable Steam Engines 350 

Stationary Engines 352 

Steam Fire Engines 362 

Steam Excavator 371 

CHAP. XII.— Manufacture and Management op Steam Engines. 

Construction of Engines 378 

Erection of Engines 388 

Management of Marine Boilers 395 

Management of Marine Engines 399 

Management of Locomotives 403 




MECHAKECAL PRmCIPLES 



THE STEAM ENGINE. 



CLASSIFICATION OF ENGINES. 



1. Q, — What is meant by a vacuum ? 

A. — A vacuum means an empty space ; a space in wMch 
there is neither water nor air, nor anything else that we know 
of. 

2. Q. — Wherein does a high pressure differ from a low pres- 
sure engine ? - 

A. — In a high pressure engine the steam, after having pushed 
the piston to the end of the stroke, escapes into the alktt|^ere, 
and the impelling force is therefore that due to the oMBfece 
between the pressure of the steam and the pressure of the at- 
mosphere. In the condensing engine the steam, after having 
pressed the piston to the end of the stroke, passes into the con- 
denser, in which a vacuum is maintained, and the impelling 
force is that due to the difference between the pressure of the 
steam above the piston, and the pressure of the vacuum beneath 
it, which is nothing ; or, in other words, you have then the 
whole pressure of the steam urging the piston, consisting of the 
pressure shown by the safety-valve on the boiler, and the pres- 
sure of the atmosphere besides. 

3. Q, — In what way would you class the various kinds of 
condensing engines ? 



2 CLASSIFICATION OF ENGINES. 

A, — Into single acting, rotative, and rotatory engines. Single 
acting engines are engines without a crank, such as are used for 
pumping water. Rotative engines are engines provided with a 
crank, by means of which a rotative motion is produced ; and 
in this important class stand marine and mill engines, and all 
engines, indeed, in which the rectilinear motion of the piston is 
changed into a circular motion. In rotatory engines the steam 
acts at once in the production of circular motion, either upon 
a revolving piston or otherwise, but without the use of any in- 
termediate mechanism, such as the crank, for deriving a circular 
from a rectilinear motion. Rotatory engines have not hitherto 
been very successful, so that only the single acting or pumping 
engine, and the double acting or rotative engine can be said to 
be in actual use. For some purposes, such, for example, as 
forcing air into furnaces for smelting iron, double acting engines 
are employed, which are nevertheless unfurnished with a crank ; 
but engines of this kind are not sufficiently numerous to justify 
their classification as a distinct species, and, in general, those 
engines may be considered to be single acting, by which no 
rotatory motion is imparted. 

4. §. — Is not the circular motion derived from a cylinder 
engine very irregular, in consequence of the unequal leverage 
of the crank at the different parts of its revolution ? 

A, — No ; rotative engines are generally provided with a fly- 
wheel to correct such irregularities by its momentum ; but 
where two engines with their respective cranks set at right 
angles are employed, the irregularity of one engine corrects 
that of the other with sufficient exactitude for many purposes. 
In the case of marine and locomotive engines, a fly-wheel is not 
employed ; but for cotton spinning, and other purposes requir- 
ing great regularity of motion, its use with common engines is 
indispensable, though it is not impossible to supersede the 
necessity by new contrivances. 

5. §. — You implied that there is some other difference be- 
tween single acting and double acting engines, than that which 
lies in the use or exclusion of the crank ? 

A. — Yes ; single acting engines act only in one way by the 



w 



NATTJEE AND USES OP A VACUUM. 3 

force of the steam, and are returned by a counter-weiglit ; 
whereas double acting engines are urged by the steam in both 
directions. Engines, as I have already said, are sometimes made 
double acting, though unprovided with a crank ; and there 
would be no difficulty in so arranging the valves of all ordinary 
pumping engines, as to admit of this action ; for the pumps might 
be contrived to raise water both by the upward and downward 
stroke, as indeed in some mines is already done. But engines 
without a crank are almost always made single acting, perhaps 
from the effect of custom, as much as from any other reason, 
and are usually spoken of as such, though it is necessary to 
know that there are some deviations from the usual practice. 

NATUKE AND USES OF A VACUUM. 

6. Q. — The pressure of a vacuum you have stated is nothing ; 
but how can the pressure of a vacuum be said to be nothing, 
when a vacuum occasions a pressure of ISlbs. on the square 
inch ? 

A, — Because it is not the vacuum which exerts this pressure, 
but the atmosphere, which, like a head of water, presses on 
everything immerged beneath it. A head of water, however, 
would not press down a piston, if the water were admitted on 
both of its sides ; for an equilibrium would then be established, 
just as in the case of a balance which retains its equilibrium 
when an equal weight is added to each scale ; but take the 
weight out of one scale, or empty the water from one side of 
the piston, and motion or pressure is produced ; and in like 
manner pressure is produced on a piston by admitting steam 
or air upon the one side, and withdrawing the steam or air 
from the other side. It is not, therefore, to a vacuum, but 
rather to the existence of an imbalanced plenum, that the pres- 
sure made manifest by exhaustion is due, and it is obvious 
therefore that a vacuum of itself would not work an engine. 

7. Q. — How is the vacuum maintained in a condensing 
engine ? 

-4. —The steam, after having performed its office in the 



4 NATTEE A]SD USES OF A VACUUM. 

cylinder, is permitted to pass into a vessel called the condenser, 
where a shower of cold water is discharged upon it. The 
steam is condensed by the cold water, and falls in the form of 
hot water to the bottom of the condenser. The water, which 
would else be accumulated in the condenser, is continually 
being pumped out by a pump worked by the engine. This 
pump is called the air pump, because it also discharges any air 
which may have entered with the water. 

8. Q. — If a vacuum be an empty space, and there be water 
in the condenser, how can there be a vacuum there ? 

A. — There is a vacuum above the water, the water being 
only like so much iron or lead lying at the bottom. 

9. Q. — Is the vacuum in the condenser a perfect vacuum ? 
A. — Not quite perfect ; for the cold water entering for the 

purpose of condensation is heated by the steam, and emits a 
vapor of a tension represented by about three inches of mer- 
cury ; that is, when the common barometer stands at 30 inches, 
a barometer with the space above the mercury communicating 
with the condenser, will stand at about 27 inches. 

10. Q. — Is this imperfection of the vacuum wholly attributa- 
ble to the vapor in the condenser ? 

A. — No ; it is partly attributable to the presence of a small 
quantity of air which enters with the water, and which would 
accumulate until it destroyed the vacuum altogether but for the 
action of the air pump, which expels it with the water, as 
already explained. All common water contains a certain quan- 
tity of air in solution, and this air recovers its elasticity when 
the pressure of the atmosphere is taken off, just as the gas in 
soda water flies up so soon as the cork of the bottle is with- 
drawn. 

11. Q. — Is a barometer sometimes applied to the condensers 
of steam engines ? 

A. — Yes; and it is called the vacuum gauge, because it 
shows the degree of perfection the vacuum has attained. An- 
other gauge, called the steam gauge, is applied to the boiler, 
which indicates the pressure of the steam by the height to 
which the steam forces mercury up a tube. Gauges are also 



NATURE AND USES OF A VACUUM. 5 

applied to the boiler to indicate the height of the water within 
it so that it may not be burned out by the water becoming ac- 
cidentally too low. In some cases a succession of cocks placed 
a short distance above one another are employed for this pur- 
pose, and in other cases a glass tube is placed perpendicularly 
in the front of the boiler and communicating at each end with 
its interior. The water rises in this tube to the same height as 
in the boiler itself, and thus shows the actual water level. 
In most of the modern boilers both of these contrivances are 
adopted. 

12. Q, — Can a condensing engine be worked with a pressure 
less than that of the atmosphere ? 

A, — Yes, if once it be started; but it will be a difficult 
thing to start an engine, if the pressure of the steam be not 
greater than that of the atmosphere. Before an engine can be 
started, it has to be blown through with steam to displace the 
air within it, and this cannot be effectually done if the pressure 
of the steam be very low. After the engine is started, however, 
the pressure in the boiler may be lowered, if the engine be 
lightly loaded, until there is a partial vacuum in the boiler. 
Such a practice, however, is not to be commended, as 
the gauge cocks become useless when there is a partial 
vacuum in the boiler ; inasmuch as, when they are opened, 
the water will not rush out, but air will rush in. It is 
impossible, also, under such circumstances, to blow out any 
of the sediment collected within the boiler, which, in the case 
of the boilers of steam vessels, requires to be done every two 
hours or oftener. This is accomplished by opening a large 
cock which permits some of the supersalted water to be forced 
overboard by the pressure of the steam. In some cases, in 
which the boiler applied to an engine is of inadequate size, the 
pressure within the boiler will fall spontaneously to a point con- 
siderably beneath the pressure of the atmosphere ; but it is pref- 
erable, in such cases, partially to close the throttle valve in 
the steam pipe, whereby the issue of steam to the engine is 
diminished ; and the pressure in the boiler is thus maintained, 
while the cylinder receives its former supply. 



6 VELOCITY OF FALLING BODIES. 

13. Q. — K a hole be opened into a condenser of a steam 
engine, will air rush into it ? 

A. — If the hole communicates with the atmosphere, the air 
will be drawn in. 

14. Q. — With what velocity does air rush into a vacuum ? 
A. — With the velocity which a body would acquire by 

falling from the height of a homogeneous atmosphere, which is 
an atmosphere of the same density throughout as at the earth's 
surface ; and although such an atmosphere does not exist in 
natur^, its existence is supposed, in order to facilitate the com- 
putation. It is well known that the velocity with which water 
issues from a cistern is the same that would be acquired by a 
body falliug from the level of the head to the level of the issu- 
ing point ; which indeed is an obvious law, since every particle 
of water descends and issues by virtue of its gravity, and is in 
its descent subject to the ordinary laws of falling bodies. Air 
rushing into a vacuum is only another example of the same 
general principle : the velocity of each particle will be that due 
to the height of the column of air which would produce the 
pressure sustained ; and the weight of air being known, as well 
as the pressure it exerts on the earth's surface, it becomes easy 
to tell what height a column of air, an inch square, and of the 
atmospheric density, would require to be, to weigh 151bs. The 
height would be 27,818 feet, and the velocity which the fall of 
a body from such a height produces would be 1,338 feet per 
second. 

VELOCITY OF FALLING BODIES AND MOMENTUM OF MOVING 

BODIES. 

15. Q. — How do you determine the velocity of falling bodies 
of different kinds ? 

A, — All bodies fall with the same velocity, when there is 
no resistance from the atmosphere, as is shown by the experi- 
ment of letting fall, from the top of a tall exhausted receiver, a 
feather and a guinea, which reach the bottom at the same time. 
The velocity of falling bodies is one that is accelerated uniform- 
ly, according to a known law. When the height from which a 



TELOCITY OF FALLING BODIES. 7 

body falls is given, the velocity acquired at the end of the 
descent can be easily computed. It has been found by experi- 
ment that the square root of the height in feet multiplied by 
8*021 will give the velocity. 

16. Q, — But the velocity in what terms ? 

A. — In feet per second. The distance through which a body 
falls by gravity in one second is 16y^2 ^^^* ? ^ ^^ seconds, 
64,^2 ^^^^'t ill three seconds, 144^2 ^'^^\ ^^ foiir seconds, 25 Ty^ 
feet, and so on. If the number of feet fallen through in one 
second be taken as unity, then the relation of the times to the 
spaces will be as follows : — 

Number of seconds 123j4!5!6 

Units of space passed through . . . 1 4 9 !l6i25i36 



&c. 



so that it appears that the spaces passed through by a falling 
body are as the squares of the times of falling. 

17. Q. — Is not the urging force which causes bodies to fall 
the force of gravity ? 

A. — ^Yes ; the force of gravity or the attraction of the earth. 

18. Q, — ^And is not that a uniform force, or a force acting 
with a uniform pressure ? 

^.— It is. 

19. Q. — Therefore during the first second of falling as much 
impelling power will be given by the force of gravity as during 
every succeeding second ? 

A, — Undoubtedly. 

20. Q. — How comes it, then, that while the body falls 64-j-\ 
feet in two seconds, it falls only 16y^ feet in one secohd ; or why, 
since it falls only IGyg ^^et in one second, should it fall more 
than twice 16^^2 ^^^^ ^^ ^^^ • 

A. — Because 16^^ feet is the average and not the maximum 
velocity during the first second. The velocity acquired at the 
end of the 1st second is not 16^*2, but 32^ feet per second, and at 
the end of the 2d second a velocity of 32| feet has to be added ; 
60 that the total velocity at the end of the 2d second becomes 
64| feet ; at the end of the 3d, the velocity becomes 96^ feet, at 
the end of the 4th, 128| feet, and so on. These numbers pro- 



8 RULES FOR DIMENSIONS OF FLY-WHEEL RIMS. 

ceed in the progression 1, 3, 3, 4, &c., so that it appears that 
the velocities acquired by a falling body at different points, are 
simply as the times of falling. But if the velocities be as the 
times, and the total space passed through be as the squares of 
the times, then the total space passed through must be as the 
squares of the velocity ; and as the vis viva or mechanical power 
inherent in a falling body, of any given weight, is measurable 
by the height through which it descends, it follows that the 
vis viva is proportionate to the square of the velocity. Of two 
balls therefore, of equal weight, but one moving twice as fast as 
the other, the faster ball has four times the energy or mechani- 
cal force accumulated in it that the slower ball has. If the 
speed of a fly-wheel be doubled, it has four times the vis viva 
it possessed before — vis viva being measurable by a reference to 
the height through which a body must have fallen, to acquire 
the velocity given. 

21. Q, — By what considerations is the vis vica or mechanical 
energy proper for the fly-wheel of an engine determined ? 

A, — By a reference to the power produced every half-stroke 
of the engine, joined to the consideration of what relation the 
energy of the fly-wheel rim must have thereto, to keep the ir- 
regularities of motion within the limits which are admissible. 
It is found in practice, that when the power resident in- the fly- 
wheel rim, when the engine moves at its average speed, is from 
two and a half to four times greater than the power generated 
by the engine in one half-stroke — the variation depending on 
the energy inherent in the machinery the engine has to drive 
and the equability of motion required — the engine will work 
with suflicient regularity for most ordinary purposes, but where 
great equability of motion is required, it will be advisable to 
make the power resident in the fly-wheel equal to six times the 
power generated by the engine in one half-stroke. 

22. Q. — Can you give a practical rule for determining the 
proper quantity of cast iron for the rim of a fly-wheel in ordi- 
nary land engines ? 

A, — One rule frequently adopted is as follows: — Multiply 
the mean diameter of the rim by the number of its revolutions 



CENTKAL FORCES. 9 

per minute, and square tlie product for a divisor ; divide the 
number of actual horse power of the engine by the number of 
strokes the piston makes per minute, multiply the quotient by 
the constant number 2,760,000, and divide the product by the 
divisor found as above ; the quotient is the requisite quantity 
of cast iron in cubic feet to form the fly-wheel rim. 

23. Q. — ^What is Boulton and Watt's rule for finding the di- 
mensions of the fly-wheel ? 

A, — ^Boulton and Watt's rule for finding the dimensions of 
the fly-wheel is as follows : — Multiply 44,000 times the length 
of the stroke in feet by the square of the diameter of the cylin- 
der in inches, and divide the product by the square of the 
number of revolutions per minute multiplied by the cube of the 
diameter of the fly-wheel in feet. The resulting number will Jse 
the sectional area of the rim of the fly-wheel in square inches. 

CENTRAL rOKCES. 

24. Q. — What do you understand by centrifugal and cen- 
tripetal forces ? 

A, — By centrifugal force, I understand the force with which 
a revolving body tends to fly from the centre ; and by centrip- 
etal force, I understand any force which draws it to the centre, 
or counteracts the centrifugal tendency. In the conical pendu- 
lum, or steam engine governor, which consists of two metal 
balls suspended on rods hung from the end of a vertical revolv- 
ing shaft, the centrifugal force is manifested by the divergence 
of the balls, when the shaft is put into revolution ; and the cen- 
tripetal force, which in this instance is gravity, predominates so 
soon as the velocity is arrested ; for the arms then collapse and 
hang by the side of the shaft. 

25. ^.— What measures are there of the centrifugal force of 
bodies revolving in a circle ? 

A. — The centrifugal force of bodies revolving in a circle in- 
creases as the diameter of the circle, if the number of revolu- 
tions remain the same. If there be two fly-wheels of the same 
weight, and making the same number of revolutions per minute, 



10 CENTRIFUGAL AND CENTRIPETAL FORCES. 

but the diameter of one be double that of the other, the larger 
will have double the amount of centrifugal force. The centrif- 
ugal force of the same wheel^ however, increases as the square 
of the velocity ; so that if the velocity of a fly-wheel be doubled, 
it will have four times the amount of centrifugal force. 

26. §. — Can you give a rule for determining the centrifugal 
force of a body of a given weight moving with a given velocity 
in a circle of a given diameter ? 

A, — ^Yes. If the velocity in feet per second be divided by 
4*01, the square of the quotient will be four times the height in 
feet from which a body must have fallen to have acquired that 
velocity. Divide this quadruple height by the diameter of the 
circle, and the quotient is the centrifugal force in terms of the 
weight of the body, so that, multiplying the quotient by the 
actual weight of the body, we have the centrifugal force in 
pounds or tons. Another rule is to multiply the square of the 
number of revolutions per minute by the diameter of the circle 
in feet, and to divide the product by 5,870. The quotient is the 
centrifugal force in terms of the weight of the body. 

27. §. — How do you find the velocity of the body when its 
centrifugal force and the diameter of the circle in which it 
moves are given ? 

A. — ^IVIultiply the centrifugal force in terms of the weight of 
the body by the diameter of the circle in feet, and multiply the 
square root of the product by 4*01 ; the result will be the velo- 
city of the body in feet per second. 

28. Q,. — Will you illustrate this by finding the velocity at 
which the cast iron rim of a fly-wheel 10 feet in diameter 
would burst asunder by its centrifugal force ? 

A, — If we take the tensile strength of cast iron at 15,000 
lbs. per square inch, a fly-wheel rim of one square inch of sec- 
tional area would sustain 30,000 lbs. If we suppose one half of 
the rim to be so flxed to the shaft as to be incapable of detach- 
ment, then the centrifugal force of the other half of 'the rim at 
the moment of rupture must be equal to 30,000 lbs. Now 
30,000 lbs. divided by 49-48 (the weight of the half rim) is equal 
to 606*3, which is the centrifugal force in terms of the weight. 



BURSTING VELOCITY OF FLY-WHEELS. 11 

Then by the ruk given in the last answer 606-3 x 10 = 6063, the 
square root of which is 78 nearly, and 78 x 4*01 = 312*78, the 
velocity of the rim in feet per second at the moment of rupture. 

29. Q, — What is the greatest velocity at which it is safe 
to drive a cast iron fly-wheel ? 

A. — If we take 2,000 lbs. as the utmost strain per square 
inch to which cast iron can be permanently subjected with 
safety ; then, by a similar process to that just explained, we 
have #,000 lbs. -5- 49*48 = 80*8 which multiplied by 10 = 808, 
the square root of which is 28*4, and 28-4 x 4*01 = 113*884, 
the velocity of the rim in feet per second, which may be con- 
sidered as the highest consistent with safety. Indeed, this 
limit should not be approached in practice on account of the 
risks of fracture from weakness or imperfections in the metal. 

30. Q. — ^What is the velocity at which the wheels of railway 
trains may run if we take 4,000 lbs. per square inch as the 
greatest strain to which malleable iron should be subjected ? 

A. — The weight of a malleable iron rim of one square inch 
sectional area and 7 feet diameter is 21*991 feet x 3*4 lbs. = 
74*76, one half of which is 37*4 lbs. Then by the same process 
as before, 8,000 -s- 37*4 =213*9, the centrifugal force in terms 
of the weight: 213*9 x 7, the diameter of the wheel = 1497*3, 
the square root of which, 38*3 x 4*01 = 155*187 feet per second, 
the highest velocity of the rims of railway carriage wheels that 
is consistent with safety. 155*187 feet per second is equivalent 
to 105*8 miles an hour. As 4,000 lbs. per square inch of sec- 
tional area is the utmost strain to which iron should be exposed 
in machinery, railway wheels can scarcely be considered safe at 
speed even considerably under 100 miles an hour, unless so con- 
structed that the centrifugal force of the rim will be counteract- 
ed, to a material extent, by the centripetal action of the arms. 
Hooped wheels are very unsafe, unless the hoops are, by some 
process or other, firmly attached to the arms. It is of no use 
to increase the dimensions of the rim of a wheel with the view 
of giving increased strength to counteract the centrifugal force, 
as every increase in the weight of the rim will increase the cen- 
trifugal force in the same proportion. 



12 CENTKES OF GEAVITYj GYRATION, AND OSCILLATION. 



CENTRES OF GRAVITY, GYRATION, AND OSCILLATION. 

31. Q, — What do you understand by tlie centre of gravity 
of a body ? 

A. — That point within it, in which the whole of the weight 
may be supposed to be concentrated, and which continually 
endeavors to gain the lowest possible position. A body hung 
in the centre of gravity will remain at rest in any position. 

32. Q. — ^What is meant by the centre of gyration ? 

A. — The centre of gyration is that point in a revolving body 
in which the whole momentum may be conceived to be concen- 
trated, or in which the whole effect of the momentum resides. 
If the ball of a governor were to be moved in a straight line, the 
momentum might be said to be concentrated at the centre of 
gravity of the ball ; but inasmuch as, by its revolution round an 
axis, the part of the ball furthest removed from the axis moves 
more quickly than the part nearest to it, the momentum cannot 
be supposed to be concentrated at the centre of gravity, but at 
a point further removed from the central shaft, and that point is 
what is called the centre of gyration. 

33. Q. — What is the centre of oscillation ? 

A. — The centre of oscillation is a point in a pendulum or 
any swinging body, such, that if all the matter of the body were 
to be collected into that point, the velocity of its vibration 
would remain unaffected. It is in fact the mean distance from 
the centre of suspension of every atom, in a ratio which happens 
not to be an arithmetical one. The centre of oscillation is 
always in a line passing through the centre of suspension and 
the centre of gravity. 

THE PENDULUM AND GOVERNOR. 

34. Q, — By what circumstance is the velocity of vibration 
of a pendulous body determined ? 

A, — By the length of the suspending rod only, or, more cor- 
rectly, by the distance between the centre of suspension and the 
centre of oscillation. The length of the arc described does not 



LAW OF VIBRATIONS OF PENDULUM. 13 

signify, as the times of vibration will be tbe same, whether the 
arc be the fourth or the four hundredth of a circle, or at least 
they will be nearly so, and would be so exactly, if the curve 
described were a portion of a cycloid. In the pendulum of 
clocks, therefore, a small arc is preferred, as there is, in that 
case, no sensible deviation from the cycloidal curve, but in 
other respects the size of the arc does not signify. 

35. Q^ — If then the length of a pendulum be given, can the 
numl^r of vibrations in a given time be determined ? 

a'— Yes ; the time of vibration bears the same relation to 
the time in which a body would fall through a space equal to 
half the length of the pendulum, that the circumference of a 
circle bears to its diameter. The number of vibrations made in 
a given time by pendulums of different lengths, is inversely as 
the square roots of their lengths. 

36. Q, — Then when the length of the second's pendulum is 
known the proper length of a pendulum to make any given 
number of vibrations in the minute can readily be computed ? 

A. — ^Yes ; the length of the second's pendulum being known, 
the length of another pendulum, required to perform any given 
number of vibrations in the minute, may be obtained by the 
following rule : multiply the square root of the given length by 
60, and divide the product by the given number of vibrations 
per minute ; the square of the quotient is the length of pendu- 
lum required. Thus if the length of a pendulum were required 
that would make 70 vibrations per minute in the latitude of 

London, then V 39-1393 x 60 ^ ^^^, co ^^ • i • -u • x-u 

' ^ -r =:5-363''=28-75 m., which is th< 

length required, 

37. Q. — Can you explain how it comes that the length of a 
pendulum determines the number of vibrations it makes in a 
given time ? 

A. — Because the length of the pendulum determines the 
steepness of the circle in which the body moves, and it is ob- 
vious, that a body will descend more rapidly over a steep in- 
clined plane, or a steep arc of a circle, than over one in which 
there is but a slight inclination. The impelling force is gravity, 
2 



14 RELATIONS OF PENDULUM AND GOVERNOR. 

wliicli urges the body \\ith. a force ]3roportionate to the dis- 
tance descended, and if the velocity due to the descent of a 
body through a given height be spread over a great horizontal 
distance, the speed of the body must be slow in proportion to 
the greatness of that distance. It is clear, therefore, that as the 
length of the pendulum determines the steepness of the arc, it 
must also determine the velocity of vibration. 

38. Q, — If the motions of a pendulum be dependent on the 
sj)eed with which a body falls, then a certain ratio must subsist 
between the distance through which a body falls in a second, 
and the length of the second's pendulum ? 

A. — And so there is ; the length of the second's pendulum 
at the level of the sea in London, is 39-1393 inches, and it is 
from the length of the second's pendulum that the space 
through which a body falls in a second has been determined. 
As the time in which a pendulum vibrates is to the time in 
which a heavy body falls through half the length of the pendu- 
lum, as the circumference of a circle is to its diameter, and as 
the height through which a body falls is as the square of the 
time of falling, it is clear that the height through which a body 
will fall, during the vibration of a pendulum, is to half the 
length of the pendulum as the square of the circumference of a 
circle is to the square of its diameter ; namely, as 9-8696 is to 1, 
or it is to the whole length of the pendulum as the half of this, 
namely, 4*9348 is to 1 ; and 4*9348 times 39-1393 in. is 16j\ ft. 
very nearly, which is the space through which a body falls by 
gravity in a second. 

39. Q. — Are the motions of the conical pendulum or governor 
reducible to the same laws which apply to the common pen- 
dulum ? 

-4. — Yes ; the motion of the conical pendulum may be sup- 
posed to be compounded of the motions -of two common pen- 
dulums, vibrating at right angles to one another, and one revo- 
lution of a conical j)endulum wil! be performed in the same 
time as two vibrations of a common pendulum, of which the 
length is equal to the vertical height of the point of suspension 
Sibovo the i)lane of revolution of the balls. * 



OPERATION OF THE GOVERNOR. 



15 



40. Q. — Is not tlie conical pendulum or governor of a steam 
engine driven by the engine ? 

^.— Yes. 

41. Q, — Then will it not be driven round as any other mech- 
anism would be at a speed proportional to that of the engine ? 

^.— It wiU. 

43. Q. — Then how can the length of the arms affect the 
time of revolution ? 

A,^Bj flying out until they assume a vertical height 
answering to the velocity with which they rotate round the 
central axis. As the speed is increased the balls expand, and 
the height of the cone described by the arms is diminished, 
until its vertical height is such that a pendulum of that length 
would perform two vibrations for every revolution of the gover- 
nor. By the outward niotion of the arms, they partially shut 
off the steam from the engine. If, therefore, a certain expan- 
sion of the balls be desired, and a certain length be fixed upoi^ 
for the arms, so that the vertical height of the cone is fixed, 
then the speed of the governor must be such, that it will 
make half the number of revolutions in a given time that a 



Fig. 1. 




pendulum equal in length to the height of the cone would 
m.ake of vibrations. The rule is, multiply the square root 
of the height of the cone in inches by 0-31986, and the 



16 OPERATION OF THE GOVERNOR. 

product will be the right time of revolution in secoiicls. If 
the number of revolutions and the length of the arms be 
fixed, and it is wanted to know what is the diameter of the 
circle described by the balls, you must divide the constant num- 
ber 187*58 by the number of revolutions per minute, and the 
square of the quotient will be the vertical height in inches of 
the centre of suspension above the plane of the balls' revolution. 
Deduct the square of the vertical height in inches from the 
square of the length of the arm in inches, and twice the square 
root of the remainder is the diameter of the circle in which the 
centres of the balls revolve. 

43. Q, Cannot the operation of a governor be deduced mere- 
ly from the consideration of centrifugal and centripetal forces ? 

A. — It can ; and by a very simple process. The horizontal 
distance of the arm from the spindle divided by the vertical 
height, will give the amount of centripetal force, and the velo- 
city of revolution requisite to produce an equivalent centrifugal 
force may be found by multiplying the centripetal force of the 
ball in terms of its own weight by 70,440, and dividing the 
product by the diameter of the circle made by the centre of the 
ball in inches ; the square root of the quotient is the number of 
revolutions per minute. By this rule you fix the length of the 
arms, and the diameter of the base of the cone, or, what is the 
same thing, the angle at which it is desired the arms shall 
revolve, and you then make the speed or number of revolutions 
such, that the centrifugal force will keep the balls in the de- 
sired position. 

44. Q.— Does not the weight of the balls affect the question ? 
^- — Not in the least ; each ball may be supposed to be made 

up of a number of small balls or particles, and each particle of 
matter will act for itself. Heavy balls attached to a governor 
are only requisite to overcome the friction of the throttle valve 
which shuts off the steam, and of the connections leading there- 
to. Though the weight of a ball increases its centripetal force, 
it increases its centrifugal force in the same proportion. 



THE MECHANICAL POWEKS. 17 



THE MECHANICAL POWERS. 

45. Q. — What do you understand by the mechanical 
powers ? 

A, — The mechanical powers are certain contrivances, such 
as the wedge, the screw, the inclined plane, and other elemen- 
tary machines, which convert a small force acting through a 
great space into a great force acting through a small space. In 
the school treatises on mechanics, a certain number of these de- 
vices are set forth as the mechanical powers, and each separate 
device is treated as if it involved a separate principle ; but not 
a tithe of the contrivances which accomplish the stipulated end 
are represented in these learned works, and there is no very ob- 
vious necessity for considering the principle of each contri- 
vance separately when the principles of all are one and the 
same. Every p^pssure acting with a certain velocity, or through 
a certain space, is convertible into a greater pressure acting 
with a less velocity, or through a smaller space ; but the quan- 
tity of mechanical force remains unchanged by its transforma- 
tion, and all that the implements called mechanical powers ac- 
complish is to effect this transformation. 

46. Q. — Is there no power gained by the lever ? 

A. — Not any : the power is merely put into another shaj^e, 
just as the contents of a hogshead of porter are the same, 
whether they be let off by an inch tap or by a hole a foot in 
diameter. There is a greater gush in the one case than the 
other, but it will last a shorter time ; when a lever is used there 
is a greater force exerted, but it acts through a shorter distance. 
It requires just the same expenditure of mechanical power to 
lift 1 lb. through 100 ft., as to lift 100 lbs. through 1 foot. A 
cylinder of a given cubical capacity will exert the same power 
by each stroke, whether the cylinder be made tall and narrow, 
or short and wide ; but in the one case it will raise a small 
weight through a great height, and in the other case, a great 
weight through a small height. 

47. Q. — Is there no loss of power by the use of the crank ? 
A, — Not any. Many persons have supposed that there was 



13 MISCONCEPTIONS OF NATURE OF TOAVER. 

a loss of power by tlie use of the crank, because at the tof) and 
bottom centres it is capable of exerting little or no j)ower ; but 
at those times there is little or no steam consumed, so that no 
waste of power is occasioned by the peculiarity. Those who 
imagine that there is a loss of power caused by the crank per- 
plex themselves by confounding the vertical with the circum- 
ferential velocity. If the circle of the crank be divided by any 
number of equidistant horizontal lines, it will be obvious that 
there must be the same steam consumed, and the same power 
expended, when the crank pin passes from the level of one line 
to the level of the other, in whatever part of the circle it may 
be, those lines being indicative of equal ascents or descents of 
the piston. But it will be seen that the circumferential velocity 
is greater vdth the same expenditure of steam when the crank 
pin approaches the top and bottom centres ; and this increased 
velocity exactly compensates for the dimini|j|ied leverage, so 
that there is the same power given out by the crank in each of 
the divisions. 

48. Q. — Have no plans been projected for gaining power by 
means of a lever ? 

A. — Yes, many plans, — some of them displaying much in- 
genuity, but all displaying a complete ignorance of the first 
principles of mechanics, which teach that power cannot be 
gained by any multiplication of levers and wheels. I have oc- 
casionally heard persons say : " You gain a great deal of power 
by the use of a capstan ; why not apply the same resource in 
the case of a steam vessel, and increase the power of your engine 
by placing a capstan motion between the engine and paddle 
wheels ? " Others I have heard say : " By the hydraulic press 
you can obtain unlimited power; why not then interpose a 
hydraulic press between the engines and the paddles?" To 
these questions the reply is sufficiently obvious. Whatever you 
gain in force you lose in velocity; and it would benefit you 
little to make the paddles revolve with ten times the force, if 
you at the same time caused them to make only a tenth of the 
number of revolutions. You cannot, by any combination of 
mechanism, get increased force and increased speed at the same 



SOUKCE OF MECHANICAL POWER. 19 

time, or increased force without diminislied speed ; and it is 
from tlie ignorance of this inexorable condition, that such 
myriads of schemes for the realization of perpetual motion, by- 
combinations of levers, weights, wheels, quicksilver, cranks, 
and other mere pieces of inert matter, have been propounded. 

49. Q. — Then a force once called into existence cannot be 
destroyed ? 

A, — No ; force is eternal, if by force you mean power, or in 
other words pressure acting though space. But if by force you 
mean mere pressure, then it furnishes no measure of power. Pow- 
er is not measurable by force but by force and velocity combined. 

50. Q. — Is not power lost when two moving bodies strike 
one other and come to a state of rest ? 

A. — No, not even then. The bodies if elastic will rebound 
from one another with their original velocity ; if not elastic 
they will sustain an alteration of form, and heat or electricity 
will be generated of equivalent value to the power which has 
disappeared. 

51. Q. — Then if mechanical power cannot be lost, and is 
being daily called into existence, must not there be a daily in- 
crease in the poWer existing in the world ? 

A. — That appears probable miless it flows back in the shape 
of heat or electricity to the celestial spaces. The source of 
mechanical power is the sun which exhales vapors that 
descend in rain, to turn mills, or which causes winds to blow 
by the unequal rarefaction of the atmosphere. It is from the 
sun too that the power comes which is liberated in a steam en- 
gine. The solar rays enable plants to decompose carbonic acid 
gas, the product of combustion, and the vegetation thus ren- 
dered possible is the source of coal and other combustible 
bodies. The combustion of coal under a steam boiler therefore 
merely liberates the power which the sun gave out thousands 
of years before. 

FEICTION. 

52. Q.— What is friction ? 

A. — Friction is the resistance experienced when one body 



20 LAWS OF FRICTION. 

is rubbed upon anotbcr body, and is supposed to be the result 
of tlie natural attraction which bodies have for one another, and 
of the interlocking of the impalpable asperities upon the sur- 
faces of all bodies, however smooth. There is, no doubt, some 
electrical action involved in its production, not yet recognized, 
nor understood ; and it is perhaps traceable to the disturbance 
of the electrical equilibrium of the particles of the body owing 
to the condensation or change of figure which all bodies must 
experience when subjected to a strain. When motion in op- 
posite directions is given to smooth surfaces, the minute asperi- 
ties of one surface must mount upon those of the other, and 
both will be abraded and worn away, in which act power must 
be expended. The friction of smooth rubbing substances is 
less when the composition of those substances is different, than 
when it is the same, the particles being supposed to interlock 
less when the opposite prominences or asperities are not coin- 
cident. 

53. Q. — Does friction increase with the extent of rubbing 
surface ? 

A. — No ; the friction, so long as there is no violent heating 
or abrasion, is simply in the proportion of the pressure keeping 
the surfaces together, or nearly so. It is, therefore, an obvious 
advantage to have the bearing surfaces of steam engines as large 
as possible, as there is no increase of friction by extending the 
surface, while there is a great increase in the durability. When 
the bearings of an engine are made too small, they very soon 
wear out. 

54. Q. — Does friction increase in the same ratio as velocity ? 
A. — No ; friction does not increase with the velocity at all, 

if the friction over a given amount of surface be considered ; 
but it increases as the velocity, if the comparison be made with 
the time during which the friction acts. Thus the friction of 
each stroke of a piston is the same, whether it makes 20 strokes 
in the minute, or 40 : in the latter case, however, there are 
t^vdce the number of strokes made, so that, though the friction 
per stroke is the same, the friction per minute is doubled. The 
friction, therefore, of any machine per hour varies as the velo- 



EXPEKIMENTS ON FEICIION. 21 

city, though the friction per revolution remains, at all ordinary 
velocities, the same. Of excessive velocities we have not suffi- 
cient experience to enable us to state with confidence whether 
the same law continues to operate among them. 

55. Q. — Can you give any approximate statement of the 
force expended in overcoming friction ? 

A. — It varies with the nature of the rubbing bodies. The 
friction of iron sliding upon iron, has generally been taken at 
about one tenth of the pressure, when the surfaces are oiled and 
then wiped again, so that no film of oil is interposed. The 
friction of iron rubbing upon brass has generally been taken 
at about one eleventh of the pressure under the same circum- 
stances ; but in machines in actual operation, where a film of 
some lubricating material is interposed between the rubbing 
surfaces, it is not more than one third of this amount or Jgd of v- 
the weight. While this, however, is the average result, the 
friction is a good deal less in some cases. Mr. Southern, in 
some experiments upon the friction of the axle of a grindstone 
—an account of which may be found in the 65th volume of the 
Philosophical Transactions — found the friction to amount to 
less than j^gth of the weight ; and Mr. Wood, in some experi- 
ments upon the friction of locomotive axles, found that by 
ample lubrication the friction may be made as little as ^\)th of 
the weight. In some experiments upon the friction of shafts 
by Mr. G. Eennie, he found that with a pressure of from 1 to 
5 cwt. the friction did not exceed gVth of the pressure when 
tallow was the unguent employed ; with soft soap it became 
^\th. The fact appears to be that the amount of the resistance 
denominated friction depends, in a great measure, upon the 
nature of the unguent employed, and in certain cases the viscidity 
of the unguent may occasion a greater retardation than the re- 
sistance caused by the attrition. In watchwork therefore, and 
other fine mechanism, it is necessary both to keep the bearing 
surfaces small, and to employ a thin and limpid oil for the purpose 
of lubrication, for the resistance caused by the viscidity of the 
unguent increases with the amount of surface, and the amount 
of surface is relatively greater in the smaller class of works. 



22 INFLUENCE OF UNGUENTS. 

56. Q. — Is a very tliin unguent preferable also for the larger 
class of bearings ? 

A. — The nature of the unguent, proper for different bearings, 
appears to depend in a great measure upon the amount of the 
pressure to which the bearings are subjected, — the hardest ungu- 
, ents being best where the pressure is greatest. The function of 
I lubricating substances is to prevent the rubbing surfaces from 
coming into contact, whereby abrasion would be produced, 
and unguents are effectual in this respect in the proportion of 
their viscidity ; but if the viscidity of the unguent be greater 
than what suffices to keep the surfaces asunder, an additional 
resistance will be occasioned ; and the nature of the unguent 
selected should always have reference, therefore, to the size of 
the rubbing surfaces, or to the pressure per square inch upon 
them. With oil the friction appears to be a minimum when 
the pressure on the surfiace of a bearing is about 90 lbs. per 
square inch. The friction from too small a surface increases 
twice as rapidly as the friction from too large a surface, added 
to which, the bearing, when the surface is too small, wears 
ra^^idly away. 

57. Q. — Has not M. Morin, in France, made some very com- 
jjlete experiments to determine the friction of surfaces of differ- 
ent kinds sliding upon one another ? 

A. — He has ; but the result does not differ materially from 
what is stated above, though, upon the whole, M. Morin, found 
the resistance due to friction to be somewhat greater than it has 
been found to be by various other engineers. When the sur- 
faces were merely wiped with a greasy cloth, but had no film 
of lubricating material interposed, the friction of brass upon 
cast iron he found to be -107, or about ,-Vth of the load, which 
was also the friction of cast iron upon oak. But when a film of 
lubricating material was interposed, he found that the friction 
w^as the same whether the surfaces were wood on metal, wood 
on wood, metal on wood, or metal on metal ; and the amount of 
the friction in such case depended chiefly on the nature of the 
unguent. With a mixture of hog's lard and olive oil interposed 
between the surfaces, the friction was usually from ^^Tyth to y^tli 
of the load, but in some cases it was only 2'j,-th of the load. 



WATER USED FOR LUBRICATIOI?^. 23 

58. Q. — May water be made to serve for purposes of lubri- 
cation ? 

A, — Yes, water will answer very well if the aurface be very 
large relatively with the pressure ; and in screw vessels whert? 
the propeller shaft passes through a long pipe at the stern, the 
stuffing box is purposely made a little leaky. The small leak- 
age of water into the vessel which is thus occasioned, keeps the 
screw shaft in this situation always wet, and this is all the 
lubrication which this bearing requires or obtains. 

59. Q. — What is the utmost pressure which may be cm- 
ployed without heating when oil is the lubricating material ? 

A. — That will depend upon the velocity. When the press- 
ure exceeds 800 lbs. per '.quare inch, however, upon the sec- 
tion of the bearing in a direction parallel with the axis, 
then the oil will be forced out and the bearing will neces- 
sarily heat. 

60. Q.— But, with a given Telocity, can you tell the limit of 
pressure which will be safe in practice ; or with a given pressure, 
can you tell the limit of velocity ? 

A. — Yes ; that may be done by the following empirical rule, 
w^hich has been derived from observations made upon bearings 
of different sizes and moving with different velocities. Divide 
the number 70,000 by the velocity of the surface of the bearing 
in feet per minute. The quotient will be the number of pounds 
per square inch of section in the line of the axis that may be 
put upon the bearing. Or, if Ave divide 70,000 by the number 
of pounds per square inch of section, then the quotient v/ill be 
the velocity in feet per minute at wlvicli the circumference of 
the bearing may work. • 

01. Q, — The number of square inches upon which the press- 
ure is reckoned, is not the circumference of the bearing multi- 
plied by its length, but the diameter of the bearing multiplied 
by its length ? 

A, — Precisely so, it will be the diameter multiphed by the 
length of the bearing. 

62. Q. — What is the amount of friction in the case of sur- 
faces sliding upon one another in sandy or muddy water — such 



24 



FRICTION OF VALVES FOR WATER. 



surfaces, for example, as are to be found in the sluices of valves 
for water ? 

A. — Various experiments have been made by Mr. Summers 
of Southampton to ascertain the friction of brass surfaces 
sliding upon each other in salt water, with the view of finding 
the power required for moving sluice doors for lock gates and 
for other similar purposes. The surfaces were planed as true 
and smooth as the planing machine would make them, but were 
not filed or scraped, and the result was as follows : 



Area of Slide rubbing 
Surface. 


Weight or Pressure on 
rubbing Surface. 


Power required to move the 

Slide slowly in muddy Salt 

Water, kept stirred up. 


Sq. in. 
8 


lb. 

56 
113 

168 
224 
336 

448 


lb. 

21-5 

44- 

65-5 

88-5 

140-5 

170-75 



Fig. 2. 
Sketch of Slide. 



4 



The facing on wliich the slide moved was similar, but three or four times as long. 

These results were the average of eight fair trials ; in each 
case, the sliding surfaces were totally immersed in muddy salt 
water, and although the apparatus used for drawing the slide 
along was not very delicately fitted up, the jDOwer required may 
be considered as a sufficient approximation for practical jDur- 
posf^s. 

It appears from these experiments, that rough surfaces follow 
the same law as regards friction that is followed by smooth, for 
in each case the friction increases directly as the pressure. 



STRENGTH OF MATERIALS. 25 



STRENGTH OF MATERIALS AND STExVINS SUBSISTING IN 
MACHINES. 

63. Q^ — In what way are tlie strengths of the different parts 
of a steam engme determmed ? 

^, — By reference to the amount of the strain or pressure to 
which they are subjected, and to the cohesive strength of the 
iron or other material of which they are composed. The strains 
subsisting in engines are usually characterized as tensile, crush- 
ing, twisting, breaking, and shearing strains ; but they may be 
all resolved into strains of extension and strains of compression ; 
and by the power of the materials to resist these two strains, 
will their practical strength be measurable. 

64. Q. — What are the ultimate strengths of the malleable 
and cast iron, brass, and other materials employed in the con- 
struction of engines ? 

A. — The tensile and crushing strengths of any given mate- 
rial are by no means the same. The tensile strength, or strength 
when extended, of good bar iron is about 60,000 lbs., or nearly 
27 tons per square inch of section; and the tensile strength of 
cast iron is about 15,000 lbs., or say 6| to 7 tons per square 
inch of section. These are the weights which are required to 
break them. The crushing strain of cast iron, however, is 
about 100,000 lbs., or 44^- tons ; whereas the crushing strength 
of malleable iron is not more than 27,000 lbs., or 12 tons, per 
square inch of section, and indeed it is generally less than this. 
The ultimate tensile strength, therefore, of malleable iron is four 
times greater than that of cast iron, but the crushing strength 
of cast iron is between three and four times greater than that of 
wrought iron. It may be stated, in round numbers, that the ten- 
sile strength of malleable iron is twice greater than its crushing 
strength ; or, in other words, that it will take twice the strain 
to break a bar of malleable iron by drawing it asunder end- 
ways, than will cripple it by forcing it together endways like a 
pillar ; whereas a bar of cast iron will be drawn asunder with 
one sixth of the force that will be required to break or cripple 
it when forced together endways like a pillar. 



2G STEENGTHS OF IKOX, STEEL, BRASS, AJN^D COPPER. 

65. Q. — What is the cohesive strength of steel ? 

A. — The ultimate tensile strength of good cast or blistered 
steel is about twice as great as that of wrought iron, being 
about 130,000 lbs. per square inch of section. The tensile 
strength of gun metal, such as is used in engines, is about 
86,000 lbs. per square inch of section ; of wrought copper about 
33,000 lbs. ; and of cast copper about 19,000 lbs. ^Dcr square 
inch of section. 

66. Q. — Is the crushing strength of steel greater or less than 
its tensile strength ? 

A. — ^It is about twice greater. A good steel punch will 
punch through a plate of wrought iron of a thickness equal to 
the diameter of the iDunch. A punch therefore of an inch 
diameter will pierce a j^late an inch tliick. Now it is well 
known, that the strain required to punch a piece of metal out 
of a plate, is just the same as that required to tear asunder a 
bar of iron of the same area of cross section as the area of the 
surface cut. The area of the surface cut in this case will be the 
circumference of the punch, 3*1416 inches, multiplied by the 
thickness of the plate, 1 inch, which makes the area of the cut 
surface 3' 1416 square inches. The area of the point of the 
j3unch subjected to the pressure is -7854 square inches, so that 
the area cut to the area crushed is as four to one. In other words, 
it will require four times the strain to crush steel that is required 
to tear asunder malleable ion, or it will take about twice the 
strain to crush steel that it will require to break it by extension. 

67. Q. — What strain may be applied to malleable iron in 
practice ? 

A. — A bar of wrought iron to which a tensile or compress- 
ing strain is applied, is elongated or contracted like a very stiff 
spiral spring, nearly in the proportion of the amount of strain 
applied up to the limit at which the strength begins to give 
way, and within this limit it will recover its original dimensions 
when the strain is removed. If, however, the strain be carried 
beyond this limit, the bar will not recover its original dimensions, 
but will be permanently pulled out or pushed in, just as would 
hai)pen to a spring to which an undue strain had been applied. 



LIMITS OP ELASTICITY. 27 

This limit is what is called the limit of elasticity ; and when- 
ever it is exceeded, the bar, though it may not break imme- 
diately, will undergo a progressive deterioration, and will break 
in the course of time. The limit of elasticity of malleable iron 
when extended, or, in other words, the tensile strain to w^hich a 
bar of malleable iron an inch square may be subjected without 
permanently deranging its structure, is usually taken at 17,800 
lbs., or from that to 10 tons, depending on the quality of the 
iron. It has also been found that malleable iron is extended 
about one ten-thousandth part of its length for every ton of 
direct strain applied to it. 

68. Q. — What is the limit of elasticity of cast iron ? 
A. — It is commonly taken at 15,300 lbs. per square inch of 
section ; but this is certainly much too high, as it exceeds the 
tensile strength of irons of medium quality. A bar of cast iron 
if compressed by weights will be contracted in length twice as 
much as a bar of malleable iron under similar circumstances ; 
but malleable iron, when subjected to a greater strain than 12 
tons per square inch of section, gradually crumples up by the 
mere continuance of the weight. A cast-iron bar one inch 
square and ten feet long, is shortened about one tenth of an 
inch by a compressing force of 10,000 lbs., whereas a malleable 
iron bar of the same dimensions would require to shorten it 
equally a compressing force of 20,000 lbs. As the load, how- 
ever, approaches 12 tons, the compressions become nearly equal, 
and above that point the rate of the compression of the malle- 
able iron rapidly increases. A bar of cast iron, when at its 
breaking point by the application of a tensile strain, is stretched 
about one six-hundredth part of its length ; and an equal strain 
employed to compress it, would shorten it about one eight- 
hundredth part of its length. 

69. Q. — But to what strain may the iron used in the con- 
struction of engines be safely subjected ? 

A. — The most of the working parts of modern engines arc 
made of malleable iron, and the utmost strain to which wrought 
iron should be subjected in machinery is 4000 lbs. per square 
inch of section. Cast iron should not be subjected to more thaii 



28 STRAIN TROPER FOR IRON IN ENGINES. 

half of this. In locomotive boilers the strain of 4000 lbs. per 
square inch of section is sometimes exceeded by nearly one 
half; but such an excess of strain approaches the limits of 
danger. 

70. Q. — Will you explain in what way the various strains 
.'subsisting in a steam engine may be resolved into tensile and 
crushing strains ; also in what way the magnitude of those 
^•trains may be determined ? 

A. — To take the case of a beam subjected to a transverse 
strain, such as the great beam of an engine, it is clear, if we 
suppose the beam broken through the middle, that the amount 
of strain at the upper and lower edges of the beam, where the 
whole strain may be supposed to be collected, will, with any 
given pressure on the piston, depend upon the proportion of 
the length to the depth of the beam. One edge of the beam 
breaks by extension, and the other edge by compression ; and 
the upper and lower edges may be regarded as pillars, one of 
which is extended by the strain, and the other is compressed. 
If, to make an extreme supposition, the depth of the beam is 
taken as equal to its length, then the pillars answering to the 
edges of the beam will be compressed, and extended by what 
is virtually a bellcrank lever with equal arms ; the horizontal 
distance from the main centre to the end of the beam being 
one of the arms, and the vertical height from the main centre to 
the top edge of the beam being the other arm. The distance, 
therefore, i^assed through by the fractured edge of the beam 
during a stroke of the engine, will be equal to the length of the 
stroke ; and the strain it will have to sustain will consequently 
be equal to the pressure on the piston. If its motion were only 
half that of the piston, as would be the case if its depth were 
made one half less, the strain the beam would have to bear 
would be twice as great ; and it may be set down as an axiom, 
that the strain upon any part of a steam engine or other 
machine is inversely equal to the strain produced by the prime 
mover, multiplied by the comparative velocity with which the 
part in question moves. If any part of an engine moves with a 
less velocity than the piston, it will have a greater strain on it, 



AGGKAVATION OF STRAIN BY BEING INTERMITTENT. 29 

if resisted, than is thrown upon the piston. If it moves with 
a greater velocity than the piston, it will have a less strain upon 
it, and the difference of strain will in every case be in the in- 
verse proportion of the difference of the velocity. 

71. Q, — Then, in computing the amount of metal necessary 
to give due strength to a beam, the first point is to determine 
the velocity with which the edge of the beam moves at that 
point were the strain is greatest ? 

A, — The web of a cast-iron beam or girder serves merely to 
connect the upper and lower edges or flanges rigidly together, 
so as to enable the extending and compressing strains to be 
counteracted in an effectual manner by the metal of those 
flanges. It is only necessary, therefore, to make the flanges of 
sufficient strength to resist effectually the crushing and tensile 
strains to which they are exposed, and to make the web of the 
beam of sufficient strength to prevent a distortion of its shape 
from taking place. 

72. Q. — Is the strain greater from being movable or inter- 
mittent than if it was stationary ? 

A, — Yes it is nearly twice as great from being movable. 
Engineers are in the habit of making girders intended to sustain 
a stationary load, about three times stronger than the breaking 
weight ; but if the load be a movable one, as is the case in the 
girders of railway bridges, they make the strength equal to six 
times the breaking weight. 

73. Q. — Then the strain is increased by the suddenness with 
which it is applied ? 

A. — If a weight be placed on a long and slender beam 
propped up in the middle, and the prop be suddenly with- 
drawn, so as to allow deflection to take place, it is clear that 
the deflection must be greater than if the load had been gradu- 
ally applied. The momentum of the weight and also of the 
beam itself falling through the space through which it has been 
deflected, has necessarily to be counteracted by the elasticity 
of the beam ; and the beam will, therefore, be momentarily 
bent to a greater extent than what is due to the load, and after 
a few vibrations up and down it will finally settle at that point 



50 INCREASE OF STEAIN DUE TO DEFLECTIOl^r. 

of deflection which the load j^i'operly occasions. It is obvious 
that a beam must be strong enough, not merely to sustain the 
pressure due to the load, but also that accession of pressure due 
to the counteracted momentum of the weight and of the beam 
itself. Although in steam engines the beam is not loaded by a 
weight, but by the pressure of the steam, yet the momentum of 
the beam itself must in every case be counteracted, and the 
momentum will be considerable in every case in which a large 
and rapid deflection takes place. A rapid deflection increases 
the amount of the deflection as well as the amount of the strain, 
as is seen in the cylinder cover of a Cornish pumping engine, 
into which the steam is suddenly admitted, and in which the 
momentum of the particles of the metal put into motion in- 
creases the deflection to an extent such as the mere pressure of 
the steam could not produce. 

74. Q. — What will be the amount of increased strain conse- 
quent upon deflection ? 

A. — The momentum of any moving body being proportional 
to the square of its velocity, it follows that the strain w^ill be 
proportional to the square of the amount of deflection produced 
in a specified time. 

75. Q. — ^But will not the inertia of a beam resist deflection, 
as well as the momentum increase deflection ? 

A, — No doubt that will be so ; but whether in practical 
cases increase of mass without reference to strength or load 
will, upon the whole, increase or diminish deflection, will 
depend very much upon the magnitude of the mass relatively 
with the magnitude of the deflecting pressure, and the rapidity 
with which that pressure is applied and removed. Thus if a 
force or weight be very suddenly applied to the middle of a 
ponderous beam, and be as suddenly withdrawn, the inertia of 
the beam will, as in the case of the collision of bodies, tend to 
resist the force, and thus obviate deflection to a considerable 
extent ; but if the pressure be so long continued as to i^roduce 
the amount of deflection due to the pressure, the efiect of the 
inertia in that case will be to increase the deflection. 

76. Q. — Will the pressure given to the beam of an engine in 
difl*ercnt directions facilitate its fracture ? 



STRENGTH OF PILLAES. 31 

A, — Iron beams bent alternately in opposite directions, or 
alternately deflected and released, will be broken in tbe course 
of time with a much less strain than is necessary to produce 
immediate fracture. It has been found, experimentally, that a 
cast-iron bar, deflected by a revolving cam to only half the 
extent due to its breaking weight, will in no case withstand 
900 successive deflections ; but, if bent by the cam to only one 
third of its ultimate deflection, it will withstand 100,000 deflec- 
tions without visible injury. Looking, however, to the jolts 
and vibrations to which engines are subject, and the sudden 
strains sometimes thrown upon them, either from water getting 
into the cylinder or otherwise, it does not appear that a strength 
answering to six times the breaking weight will give suflicient 
margin for safety in the case of cast-iron beams. 

77. §. — Does the same law hold in the case of the deflection 
of malleable iron bars ? 

A, — In the case of malleable iron bars it has been found 
that no very perceptible damage was caused by 10,000 deflec- 
tions, each deflection being such as was due to half the load 
that produced a large permanent deflection. 

78. §. — The power of a rod or pillar to resist compression 
becomes very little when the diameter is small and the length 
great ? 

A. — The power of a rod or pillar to resist compression, 
varies nearly as the fourth power of the diameter divided by the 
square of the length. In the case of hollow cylindrical columns 
of cast iron, it has been found, experimentally, that the 3-55th 
power of the internal diameter, subtracted from the 3-55th 
power of the external diameter, and divided by the l*7th power 
of the length, will represent the strength very nearly. In the 
case of hollow cylindrical columns of malleable iron, experi- 
ment shows th9.t the 3 -5 9th power of the internal diameter, 
subtracted from the 3 '5 9th power of the external diameter, and 
divided by the square of the length, gives a proper expression 
for the strength ; but this rule only holds where the strain does 
not exceed 8 or 9 tons on the square inch of section. Beyond 
12 or 13 tons per square inch of section, the metal cannot be 



32 LAW OF STRENGTH VARIES WITH THICKNESS. 

depended upon to withstand the strain, though hollow pillars 
will sometimes bear 15 or 16 tons per square inch of section. 

79. Q. — Does not the thickness of the metal of the pillars or 
tubes affect the question ? 

A. — It manifestly does ; for a tube of very thin metal, such 
as gold leaf or tin foil, would not stand on end at all, being 
crushed down by its own weight. It is found, experimentally, 
that in malleable iron tubes of the respective thicknesses of 
•525, -273, and "124 inches, the resistances per square inch of 
section are 19*17, 14*47, and 7*47 tons respectively. The power 
of plates to resist compression varies nearly as the cube, or more 
nearly as the 2-878th power of their thickness ; but this law 
only holds so long as the pressure applied does not exceed from 
9 to 12 tons per square inch of section. When the pressure is 
greater than this the metal is crushed, and a new law super- 
venes, according to which it is necessary to employ plates of 
twice or three times the thickness, to obtain twice the resisting 
power. 

80. Q. — In a riveted tube, will the riveting be much 
damaged by heavy strains ? 

A, — It will be most affected by percussion. Long-continued 
impact on the side of a tube, producing a deflection of only one 
fifth of that which would be required to injure it by pressure, 
is found to be destructive of the riveting ; but in large riveted 
structures, such as a ship or a railway bridge, the inertia of the 
mass will, by resisting the effect of impact, prevent any in- 
jurious action from this cause from taking jDlace. 

81. Q. — Will the power of iron to resist shocks be in all 
cases proportional to its power to resist strains ? 

A, — By no means. Some cast iron is very hard and brittle ; 
and although it will in this state resist compression very strong- 
ly, it will be easily broken by a blow. Iron which has been 
remelted many times generally falls into this category, as it 
will also do if run into very small castings. It has been found, 
by experiment, that iron of which the crushing weight per 
square inch is about 42 tons, will, if remelted twelve times, 
bear a crushing weight of 70 tons, and if remelted eighteen 



COMBINATION OF MALLEABLE AND CAST IRON. 33 

times it will bear a crushing weight of 83 tons ; but taking its 
power to resist impact in its first state at 706, this power will be 
raised at the twelfth remelting to 1153, and will be sunk at the 
eighteenth remelting to 149. 

82. Q. — From all this it appears that a combination of cast 
iron and malleable iron is the best for the beams of engines ? 

A, — Yes, and for all beams. Engine beams should be made 
deeper at the middle than they are now made ; the web should 
be lightened by holes pierced in it, and round the edge of the 
beam there should be a malleable iron hoop or strap securely 
attached to the flanges by riveting or otherwise. The flanges 
at the edges of engine beams are invariably made too small. It 
is in them that the strength of the beam chiefly resides. 



CHAPTER I. 

GENERAL DESCRIPTION OF THE STEAM ENGINE. 



THE BOILER. 



g3, (2- — What are the cliicf varieties of the steam engine in 
actual practical use ? 

^...^There is first the single-acting engine, which is used for 
pumping water ; the rotative land engine, which is employed to 
drive mills and manufactories; the rotative marine engine, 
which is used to propel steam vessels ; and the locomotive en- 
gine, which is employed on railways. The last is always a high- 
pressure engine ; the others are, for the most part, condensing 
engines. 

84. Q. — Will you explain the construction and action of the 
single-acting engine, used for draining mines ? 

A. — Permit me then to begin with the boiler, which is com- 
mon and necessary to all engines ; and I will take the example 
of a wagon boiler, such as was employed by Boulton and 
Watt universally in their early engines, and wliich is still in ex- 
tensive use. This boiler is a long rectangular vessel, with a 
rounded top, like that of a carrier's wagon, from its resem- 
blance to which it derives its name. A fire is set beneath it, 
arid flues constructed of brickwork encircle it, so as to keep the 



THE WAGON BOILER. 



35 



Fig.^ 



flame and smoke in contact with the boiler for a sufficient time 
to absorb the heat. 

85. Q. — This species of boiler has not an internal furnace, 
but is set in brickwork, in which the furnace is formed ? 

A. — Precisely so. The general arrangement and configura- 
tion will be at once understood by a reference to the annexed 
figure (jfig. 3), which is a transverse section of a wagon boiler. 
The line b represents the 
top of the grate or fire bars, 
which slope downward 
from the front at an angle 
of about 25°, giving the 
fuel a tendency to move to- 
ward the back of the grate. 
The supply of air ascends 
from the ash pit through the 
grate bars, and the flame 
passes over a low wall or 
bridge, and traverses the 
bottom of the boiler. The 
smoke rises up at the back 
of the boiler, and proceeds 
through the flue f along one 
side to the front, and re- 
turns along the other side 
of the boiler, and then as- 
cends the chimney. The 
performance of this course 
by the smoke is what is termed a wheel draught, as the smoke 
wheels once round the boiler, and then ascends the chimney. 

86. Q. — Is the performance of this course by the smoke 
universal in wagon boilers ? * 

A. — No ; such boilers sometimes have what is termed a 
split draught. The smoke and flame, when they reach the end 
of the boiler, pass in this case through an iron flue or tube, 
reaching from end to end of the boiler ; and on arriving at the 
front of the boiler, the smoke splits or separates — one half pass- 




36 THE WAGON BOILER. 

ing through a flue on the one side of the boiler, and the other 
half passing through a flue on the other side of the boiler — both 
of these flues having their debouch in the chimney. 

87. Q. — What are the appliances usually connected with a 
wagon boiler ? 

A, — On the top of the boiler, near the front, is a short cylin- 
der, with a lid secured by bolts. This is the manhole door, 
the purpose of which is to enable a man to get into the inside of 
the boiler when necessary for inspection and repair. On the 
top of this door is a small valve opening downward, called the 
atmospheric valve. The intention of this valve is to prevent a 
vacuum from being formed accidentally in the boiler, which 
might collapse it ; for if the pressure in the boiler subsides to a 
point materially below the pressure of the atmosphere, the valve 
will open and allow air to get in. A bent pipe, which rises 
up from the top of the boiler, immediately behind the position 
of the manhole, is the steam pipe for conducting the steam to 
the engine ; and a bent pipe which ascends from the top of 
the boiler, at the back end, is the waste-steam pipe for conduct- 
ing away the steam, which escapes through the safety valve. 
This valve is set in a chest, standing on the top of the boiler, 
at the foot of the waste-steam pipe, and it is loaded with iron 
or leaden weights to a point answerable to the intended press- 
ure of the steam. 

88. Q. — How is the proper level of the water in the boiler 
maintained ? 

A. — By means of a balanced buoy or float. This float is 
attached to a rod, which in its turn is attached to a lever set 
on the top of a large upright pipe. The upper part of the 
pipe is widened out into a small cistern, through a short pipe 
in the middle of which a chain passes to the damper ; but any 
water emptied into this small cistern cannot pass into the pipe, 
except through a small valve fixed to the lever to which ^the 
rod is attached. The water for replenishing the boiler is 
pumped into the small cistern on the top of the pipe ; and it 
follows from these arrangements that when the buoy falls, the 
rod opens the small valve and allows the feed water to enter 



REGULATION OF THE FIRE. 



the pipe, which communicates with the 
water in the boiler; whereas, when the 
buoy rises, the feed cannot enter the pipe, 
and it has, therefore, to run to waste 
through an overflow pipe provided for the 
purpose. 

89. Q. — How is the strength of the 
fire regulated ? 

A. — The draught through the furnaces 
of land boilers is regulated by a plate of 
metal or a damper, as it is called, which 
slides like a sluice up and down in the 
flue, and this damper is closed more or less 
when the intensity of the fire has to be 
moderated. In wagon boilers this is gen- 
erally accomplished by self-acting mech- 
anism. In the small cistern pipe, which 
is called a stand pipe, the water rises up 
to a height proportional to the pressure 
of the steam, and the surface of the water 
in this pipe will rise or fall with the flue- - 
tuations in the pressure of the steam. In 
this pipe a float is placed, whicli commu- 
nicates by means of a chain with the dam- 
per. If the pressure of the steam rises, 
the float will be raised and the damper 
closed, whereas, if the pressure in the 
boiler falls, the reverse of this action will 
take place. 

90. Q, — Are all land boilers of the 
same construction as that which you have 
just described ? 

A. — No ; many land boilers are now 
made of a cylindrical form, with one or 
two internal flues in which the furnace is 
placed. A boiler of this kind is repre- 
sented in Figs. 4 and 5, and which is the 
3 



Fifij. 



m 



I 




38 



COKNISH BOILERS. 



species of boiler principally used in Cornwall. In this boiler 
a large internal cylinder or fine runs from end to end. In the 
fore part of this cylinder the furnace is placed, and behind the 
furnace a large tube filled with water extends to the end of the 
boiler. This internal tube is connected to the bottom part of 
the boiler by a copper pipe standing vertically immediately 
behind the furnace bridge, and to the top part of the boiler by 
a bent copper pipe which stands in a vertical position near the 
end of the boiler. The smoke, after passing through the cen- 
tral flue, circulates round the sides and beneath the bottom of 
the boiler before its final escape into the chimney. The boiler 
is carefully covered over to prevent the dispersion of the heat. 

91. Q. — Will you describe the construction of the boilers 
used in steam vessels ? 

A. — These are of two classes, flue boilers and tubular boilers, 

but the latter are now 

^'°_^' most used. In the flue 

boiler the furnaces are 
set within the boiler, 
and the flues proceed- 
ing from them wind 
backwards and for- 
wards within the boil- 
er until finally they 
meet and enter the 
chimney. Figs. 6, 7, 
and 8 are difibrent 
views of the flue boilers • 
of the steamer Forth. 
There are 4 boilers (as 
shown in plan, Fig. 6), 
with 3 furnaces in each, 
or 12 furnaces in all. 
Fig. 7 is an elevation 
of 2 boilers, the one to 
the right being the 
front view, and that to the left a transverse section. Fig. 8 is 



x^2^0-- ti.l 


0- -> 


U , U ^ vJ . -'' 






1 \ 














~ \ r< ^ '■" 


u...^. ...... 


i 

1 

^^ LI/ 









FLUE BOILERS.. 



39 



a longitudinal section through 2 boilers. The direction of the 
arrows in plan and longitudinal section will explain the direc- 
tion of the smoke current. 

Fig. T. 




92. Q. — Is this arrangement different from that obtaining in 
tubular boilers ? 

Fig. 8. 

^1 




A, — ^In tubular boilers, the smoke after leaving the furnace 
just passes once through a number of small tubes and then en- 



40 



MARINE TUBULAR BOILERS. 



ters tlie cMmney. These tubes are sometimes of brass, and they 

Fig. 9. 




are usually about 3 inches in diameter, and 6 or 7 fee^ long. 

Fig. 10. Fig. 11. 





AMEKICAN BOILERS. 



41 



Figs. 9, 10, and 11 represent a marine tubular boiler ; ^g. 9 
being a vertical longitudinal section, fig. 10 half a front eleva- 
tion and half a transverse section, and ^g, 11 half a back 
elevation and half a transverse section near the end. There is a 
projecting part on the top of the boiler called the " steam 
chest," of which the purpose is to retain for the use of the 
cylinder a certain supply of steam in a quiescent state, in order 
that it may have time to clear itself of foam or spray. A steam 
chest is a usual part of all marine boilers. In fig. 9 A is the 
furnace, b the steam chest, and c the smoke box which opens 
into the chimney. The front of the smoke box is usually closed 
by doors which may be opened when necessary to sweep the 
soot out of the tubes. 

The following are some forms of American boilers : 
Figs. 12 and 13 are the transverse and longitudinal sections 
of a common form of American marine boiler. 

Figs. 14 and 15 are the front and sectional elevation of one 
of the boilers of the U. S. steamer Water Witch. 





LKjUULM 

Donoo 




Fig. 13. 




^ 



42 



AMERICAN BOILERS. 




MARINE BOILERS. 



43 



Fig. 16 is a longitudinal section of a boiler of the drop flue 
variety. For land purposes tlie lowest range of tubes is gen- 
erally omitted, and the smoke makes a last return beneath the 
bottom of the boiler. 

Figs. 17 and 18 are the transverse and longitudinal sections 
of a tubular boiler, built in 1837 by R. L. Stevens for the steam- 
boat Independence. 



44 



AMEEICAN BOILERS. 



itojiiiii|t|j^.ia!ii;iffl.aqi^r--^^ 



W''l'l 
WW 
W 




LOCOMOTIVE BOILEES. 



45 



Fig. 19 is a longitudinal section of a common wood-burning 
locomotive. 




46 watt's double-acting engine. 

THE ENGINE. 

93^ Q — The steam passes from the boiler through the steam 
pipe into the cylinder of the engine ? 

^, And presses up and down the piston alternately, being 

admitted alternately above and below the piston by suitable 
valves provided for that purpose. 

94. Q, — This reciprocating motion is all that is required in 
a pumping engine ? 

A. — The prevailing form of the pumping engine consists of 
a great beam vibrating on a centre like the beam of a pair of 
scales, and the cylinder is in connection with one end of the 
beam and the pump stands at the other end. The pump end of 
the beam is usually loaded, so as to cause it to preponderate 
when the Engine is at rest ; and the whole eflfort of the steam is 
employed in overcoming this preponderance until a stroke is 
performed, when, the steam being shut off, the heavy end of 
the beam again falls and the operation is repeated. 

95. Q. — In the double-acting engine the piston is pushed by 
the steam both ways, whereas in the single-acting engine it is 
only pushed one way ? 

A. — The structure and action of a double-acting land engine 
of the kind introduced by Mr. Watt, will be understood by a 
reference to the annexed figure (fig. 20), where an engine of this 
kind is shown in section, a is the cylinder in which a mova- 
ble piston, T, is forced alternately up and down by the alternate 
admission, to each side, of the steam from the boiler. The 
l^iston, by means of a rod called the ^Diston rod, gives motion to 
the beam v w, which by means of a heavy bar, p, called the con- 
necting rod, moves the crank, q, and with it the fly wheel, x, 
from which the machinery to be driven derives its motion. 

96. Q. — Where does the steam enter from the boiler ? 

A. — At the steam pipe, b. The throttle valve in that pipe 
is an elliptical plate of metal swivelling on a spindle passing 
through its edge from side to side, and by turning which more 
or less the opening through the pipe will be more or less closed. 
The extent to which this valve is opened or closed is deter- 



DESCRIPTION OF THE AVORKING TARTS. 



47 



mined by the governor, d, the balls of which, as they collapse 
or expand, move up or down a collar on the governor spindle, 
which motion is communicated to the throttle valve by suitable 
rods and bell-cranks. The governor, it will be seen, consists 



Fi^. 20. 




substantially of two heavy balls attaclied to arms fixed upon an 
upright shaft, which is kept in revolution by means of a cord 
driven by a pulley on the fly wheel shaft. The velocity with 



48 DESCRIPTION OJg THE CYLIJSTDER VALVES. 

wliich the balls of the governor revolve being proportional to 
that of the fly wheel, it will follow, that if by reason of too 
rapid a supply of steam, an undue speed be given to the fly 
wheel, and therefore to the balls, a divergence of the balls will 
take place to an extent corresponding to the excess of velocity, 
and this movement being communicated to the throttle valve 
it will be partly closed (see ^g. 1), the supply of steam to the 
engine will be diminished, and the velocity of its motion will 
be reduced. If, on the other hand, the motion of the engine is 
slower than is requisite, owing to a deficient supjDly of steam 
through B, then the balls, not being sufficiently affected by cen- 
trifugal force, will fall towards the vertical spindle, and the 
throttle valve, c, will be more fully opened, whereby a more 
ample supply of steam wall be admitted to the cylinder, and the 
speed of the engine will be increased to the requisite extent. 

97. Q. — The piston must be made to fit the cylinder accu- 
rately so as to prevent the passage of steam ? 

A, — The piston is accurately fitted to the cylinder, and made 
to move in it steam tight by a packing of hemp driven tightly 
into a groove or recess round the edge of the piston, and which 
is squeezed down by an iron ring held by screws. The piston 
divides the cylinder into two compartments, between which 
there is no communication by which steam or any other elastic 
fluid can j)ass. A casing set beside the cylinder contains the 
valves, by means of which the steam which impels the piston 
is admitted and Avithdrawn, as the piston commences its motion 
in each direction. The upper steam box b, is divided into 
three compartments by two valves. Above the upper steam 
valve V, is a compartment communicating with the steam pipe 
B. Below the lower valve e is another compartment communi- 
cating with a pipe called the eduction pipe, which leads down- 
v/ards from the cylinder to the condenser, in which vessel the 
steam is condensed by a jet of cold water. By the valve v, a 
communication may be opened or closed between the boiler and 
the top of the cylinder, so as to j^ermit or i^revent a supply of 
steam from the one to pass to the other. By the valve e a 
communication may be open or closed between the top of the 



ACTION OF THE CYLINDER VALVES. 49 

cylinder and the condenser, so that the steam in the top com- 
partment of the cylinder may either be permitted to escape into 
the condenser, or may be confined to the cylinder. The contin- 
uation of the steam pipe leads to the lower steam box B',which, 
like, the upper, is divided into three compartments by two 
valves v' and e', and the action of the lower valves is in all 
respects the same as that of the upper; 

98. Q. — Are all these valves connected together so that they 
act simultaneously ? 

A, — The four valves v, e, v', e' are connected by rods to a 
single handle h, which handle is moved alternately up and 
down by means of pins or tappets, placed on the rod which 
works the air pump. When the handle h is pressed down, the 
levers in connexion with it o]3en the upper exhausting valve e, 
and the lower steam valve v', and close the upper steam valve v 
and the lower exhausting valve e'. On the other hand, when 
the handle h is pressed up it opens the upper steam valve v and 
the lower exhausting valve e', and at the same time closes the 
upper exhausting valve E, and the lower steam valve v'. 

99. Q. — Where is the condenser situated ? 

A, — The condenser k is imraerged in a cistern of cold water. 
At its side there is a tube i, for the admission of water to con- 
dense the steam, and which is governed by a cock, by opening 
which to any required extent, a jet of cold water may be made 
to play in the condenser. From the bottom of the condenser a 
short pipe leads to the air pump j, and in this pipe there is a 
flap valve, called the foot valve, opening towards the air pump. 
The air pump is a pump set in the same cistern of cold water 
that holds the condenser, and it is fitted with a piston or bucket 
worked by the rod l, attached to the great beam, and fitted 
with a valve opening upw^ards in the manner of a common suck- 
ing pump. The upper part of the air pump communicates with 
a small cistern s, called the hot well, through a valve opening 
outwards and called the delivery valve. A pump m, called the 
hot water pump, lifts hot water out of the hot well to feed the 
boiler, and another pump n lifts cold water from a well or other 
source of supply, to maintain the supply of water to the cold 



50 ACTION OF THE AIR PUMP AND CONDENSER. 

water cistern, in whicli tlie condenser and air pump are 
placed. 

100. Q. — "Will you explain now the manner in which the 
engine acts ? 

A, — The piston being supposed to beat the top of the C3^1in- 
der, the handle n will be raised by the lower pin or tappet on 
the air pump rod, and the valves v and e' will be opened, and at 
the same time the other pair of valves v' and e will be closed. 
Steam will therefore be admitted above the piston and the steam 
or air which had previously filled the cylinder below the piston 
will be drawn ofi' to the condenser. It will there encounter the 
jet of cold water, which is kept constantly playing there by 
keeping the cock i sufficiently open. It will thus be imme- 
diately condensed or reduced to water, and the cylinder below 
the piston will have a vacuum in it. The steam therefore ad- 
mitted from the steam pipe through the open valve v to the top 
of the cylinder, not being resisted by pressure below, will press 
the piston to the bottom of the cylinder. As it approaches 
that position, the handle n will be struck down by the upper 
pin or tappet on the air pump rod, and the valves v and e', 
previously open, will be closed, while the valves v' and e, pre- 
viously closed, will be opened. The steam which has just 
pressed down the piston, and which now fills the cylinder 
above the piston, will then flow off, through the open valve e, 
to the condenser, where it will be immediately condensed by 
the jet of cold water; and steam from the boiler, admitted 
through the open valve v', will fill the cylinder below the pis- 
ton, and press the piston upwards. When the piston has 
reached the top of the cylinder, the lower pin on the air pump 
rod will have struck the handle upwards, and will thereby have 
closed the valves v' and e, and opened the valves v and e'. 
The piston will then be in the same situation as in the com- 
mencement, and will again descend, and so will continue to be 
driven up and down by the steam. 

101. Q. — But what becomes of the cold water wliich is let 
into the condenser to condense the steam ? 

A, — It is pumped out by the air pump in the shape of hot 



CYLINDER LID AND- PISTON ROD. 51 

water, its temperature having been raised considerably by tlie 
admixture of the steam in it. When the air pump piston 
ascends it leaves behind it a vacuum ; and the foot valve being 
relieved from all pressure, the weight of the water in the con- 
denser forces it open, and the warm water flows from the con- 
denser into the lower part of the air pump, from which its re- 
turn to the condenser is prevented by the intervening valve. 
When the air pump piston descends, its pressure on the liquid 
under it will force open the valve in it, through which the hot 
water will ascend ; and when the bucket descends to the bottom 
of the pump barrel, the warm water which was below it will all 
have passed above it, and cannot return. When the bucket 
next ascends, the water above it, not being able to return 
through the bucket valve, will be forced into the hot well 
through the delivery valve s. The hot water x)ump m, pumps 
a small quantity of this hot water into the boiler,«to compensate 
for the abstraction of the water that has passed off in the form 
of steam. The residue of the hot water runs to waste. 

102. Q. — By what expedient is the piston rod enabled to 
pass through the cylinder cover without leaking steam out of 
the cylinder or air into it ? 

^.— The hole in the cylinder lid, through which the piston 
rod passes, is furnished with a recess called a stuffing box, into 
which a stuffing or packing of plaited hemp is forced, which, 
pressing on the one side against the interior of the stuffing box, 
and on the other side against the piston rod, which is smooth 
and polished, prevents any leakage in this situation. The pack- 
ing of this stuffing box is forced down by a ring of metal 
tightened by screws. This ring, which accurately fits the piston 
rod, has a projecting flange, through which bolts pass for tight- 
ening the ring down upon the packing ; and a similar expedient 
is employed in nearly every case in which packing is employed. 

103. Q, — In what way is the piston rod connected to the 
great beam ? 

^.— The piston rod is connected to the great beam by means 
of two links, one at each side of the beam shown at/ g, (fig. 21.) 
These links are usually made of the same length as the crank, 



52 THE PARALLEL MOTION. 

and theii- i3urpose is to enable tlie end of the great beam to move 
in tlie arc of a circle wMle the piston rod maintains the vertical 
position. The point of junction, therefore, of the links and the 
piston rod is of the form of a knuckle or bend at some parts of 
the stroke. 

104. Q. — But what compels the top of the piston rod to 
maintain the vertical position ? 

A. — Some engines have guide rods set on each side of the 
piston rod, and eyes on the top of the piston rod engage these 
guide rods, and maintain the piston rod in a vertical position in 
every part of the stroke. More commonly, however, the desired 
end is attained by means of a contrivance called the parallel 
motion. 

105. §.— What is the parallel motion ? 

A, — The parallel motion is an arrangement of jointed rods, 
so connected together that the divergence from the vertical line 
at any point in the arc described by the beam is corrected by an 
equal and opposite divergence due to the arc performed by the 
jointed rods during the stroke ; and as these opposite devia- 
tions mutually correct one another, the result is that the piston 
rod moves in a vertical direction. 

106. Q. — Will you explain the action more in detail ? 

A, — The pin, ^l^ 21,which passes through the end of the beam at 
/has a link/<7 hung on each side of the beam, and a short cross bar, 
called a cross head, extends from the bottom of one of these links 
to the bottom of the other, which cross head is perforated with 
a hole in the middle for the reception of the piston rod. There 
are similar links 1) d at the point of the main beam, where the 
air pump rod is attached. There are two rods d g connecting 
the links 1) d with the links/ ^, and these rods, as they always 
continue parallel to the main beam throughout the stroke, are 
called parallel lars. Attached to the end of these two rods at 
d are two other rods c d^ of which the ends at c are attached to 
stationary pins, while the ends at d follow the motion of the 
lower ends of the links 1) d. These rods are called the radius 
hars. Now it is obvious that the arc described by the point d^ 
with c as a centre, is oj^posite to the arc described by the point 



ACTION OF THE CRANK. 



53 



g with c? as a centre. The rod d g is, therefore, drawn back 
horizontally by the arc described at d to an extent equal to the 



Fig. 21. 




versed sine of the arc described at g^ or, in other words, the line 
described by the point g becomes a straight line instead of a 
curve. 

107. Q — Does the air pump rod move vertically as well as 
the piston rod ? 

A. — It does. The air pump rod is suspended from a cross 
head, passing from the centre of one of the links 1) d to the 
centre of the other link, on the opposite side of the beam. Now, 
as the distance from the central axis of the great beam to the 
point Z> is equal to the length of the rod c cZ, it will follow that 
the upper end of the link will follow one arc, and the lower end 
an equal and opposite arc. A point in the centre of the link, 
therefore, where these opposite motions meet, will follow no arc 
at all, but will move up and down vertically in a straight line. 

108. Q. — The use of the crank is to obtain a circular motion 
from a reciprocating motion ? 

A, — That is the object of it, and it accomplishes its object 
in a very perfect manner, as it gradually arrests the velocity of 
the piston towards the end of the stroke, and thus obviates 
what would otherwise be an injurious shock upon the machine. 
When the crank approaches the lowest part of its throw, and at 



54 ACTION OF THE FLY WHEEL. 

the same time the i)istou is approaching the top of the cylinder, 
the motion of the crank becomes nearly horizontal, or, in other 
words, the piston is only advanced through a very short dis- 
tance, for any given distance measured on the circle described 
by the crank pin. . Since, then, the velocity of rotation of the 
crank is nearly uniform, it will follow that the piston will move 
very slowly as it approaches the end of the stroke ; and the pis- 
ton is brought to a state of rest by this gradually retarded mo- 
tion, both at the top and the bottom of the stroke. 

109. §. — ^What causes the crank to revolve at a uniform 
velocity ? 

A, — The momentum of the machinery moved by the piston, 
but more especially of the fly wheel, which by its operation re- 
dresses the unequal pressures communicated by the crank, and 
compels the crank shaft to revolve at a nearly uniform velocity. 
Everyone knows that a heavy wheel if put into rapid rotation 
cannot be immediately stopped. At the beginning and end of 
the stroke when the crank is vertical, no force of torsion can be 
exerted on the crank shaft by the crank, but this force is at its 
maximum when the crank is horizontal. From the vertical 
point, where this force is nothing, to the horizontal point, 
where it is at its maximum, the force of torsion exerted on the 
crank shaft is constantly varying ; and the fly wheel by its mo- 
mentum redresses these irregularities, and carries the crank 
through that " dead point," as it is termed, where the piston 
cannot impart any rotative force. 

110. Q. — Are the configuration and structure of the steam 
engine, as it left the hand of Watt, materially different from 
those of modern engines ? 

A. — There is not much difTerencc. In modern rotative land 
engines, the valves for admitting the steam to the cylinder or 
condenser, instead of being clack or pot-lid valves moved by 
tappets on the air pump rod, arc usually sluice or sliding valves, 
moved by an eccentric wheel on the crank shaft. Sometime^ 
the beam is discarded altogether, and malleable iron is more 
largely used in the construction of engines instead of the cast 
iron, which formerly so largely prevailed. But upon the whole 



VARIETIES OF THE MARINE ENGINE. 



55 



tlie steam engine of the present day is substantially the engine 
of Watt ; and he who perfectly understands the operation of 
Watt's engine, will have no difficulty in understanding the oper- 
ation of any of the numerous varieties of engines since intro- 
duced. 



THE MARINE ENGINE. 

111. Q. — Will you describe the principal features of the 
kind of steam engine employed for the propulsion of vessels ? 

A. — Marine engines are of two kinds, — paddle engines and 
screw engines. In the one case the propelling instrument is 
paddle wheels kept in rotation at each side of the ship : in the 
other case, the propelling instrument is a screw, consisting of 
two or more twisted vanes, revolving beneath the water at the 
stern. Of each class of engines there are many distinct varieties. 

112. Q. — Wliat are the principal varieties of the paddle 
engine ? 

^.— There is the side lever engine {^g. 26), and the oscillat- 

Fig. 23. 



Fig. 22. 




56 



THE GORGON ENGINE. 



ing engine (fig. 27), besides numerous otiier forms of engine 
wMcli are less known or employed, such as the trunk (fig. 22), 
double cylinder (fig. 23 ), annular, Gorgon (fig. 24), steeple 
(fig. 25), and many others. The side lever engine, howevej^ 

Fig. 24. 




and the oscillating engine, are the only kinds of paddle engines 
which have been received with wide or general favor. 

113. Q. — Will you exjjlain the main distinctive features of 
the side lever engine ? 

A. In all paddle vessels, whatever be their subordinate 

characteristics, a great shaft of wTought iron, s, turned round 
by the engine, has to be carried from side to side of the vessel 



THE SIDE LEVER ENGINE. 



51 



on which shaft are fixed the paddle wheels. The paddle 
wheels may either be formed with fixed float boards for en- 
gaging the water, like the boards of a common undershot 
water wheel, or they may be formed with featJwring float 
boards as they are termed, which is float boards movable on a 
centre, and so governed by appropriate mechanism that they 
enter and leave the water in a nearly vertical position. The 
common fixed or radial floats, 
however, are the kind most ^^' * 

widely employed, and they 
are attached to the arms of 
two or more rings of mallea- 
ble iron which are fixed by 
appropriate centres on the 
paddle shaft. It is usual in 
steam vessels to employ two 
engines, the cranks of which 
are set at right angles with 
one another. When the pad- 
dle wheels are turned by the 
engines, the float boards en- 
gaging the water cause a for- 
ward thrust to be imparted to 
the shaft, which propels for- 
ward the vessel on the same 
principle that a boat is pro- 
pelled by the action of oars. 

114. Q. — These remarks 
apply to all paddle vessels ? 

A, — They do. With respect to the side lever engine, it may 
be described to be such a modification of the land beam engine 
already described, as will enable it to be got below the deck of 
a vessel. With this view, instead of a single beam being placed 
overhead, two beams are used, one of which is set on each side 
of the engine as low down as possible. The cross head which 
engages the piston rod is made somewhat longer than the diam- 
eter of the cylinder, and two great links or rods proceed one 




58 



EXAMPLE OF A SIDE LEYER ENGINE. 



from each end of the cross head to one of the side levers or 
beams. A similar cross bar at the other end of the beams 
serves to connect them together and to the connecting rod 
which, j)roceeding from thence upwards, engages the crank, 
and thereby tm-ns romid the paddle wheels. 

115. Q. — "Will you further illustrate this general description 
by an example ? 




^-^^"^ 



A. — Fig. 2G is a side elevation of a side lever engine ; x x 
represent the beams or keelsons to which the engines are at- 
tached, and on which the boilers rest. The engines arc tied 



MODE OF STARTIJifG A MARINE ENGINE. 59 

down by strong bolts passing througli tbe bottom of the vessel, 
but the boiler keeps its position by its weight alone. The 
condenser and air pump are worked off the side levers by 
means of side rods and a cross head. A strong gudgeon, called 
the main centre^ passes through the condenser at k, the project- 
ing ends of which serve to support the side levers or beams. 
L is the piston rod, which, by means of the cross head and side 
rods, is connected to the side levers or beams, one of which is 
shown at h h. The line m represents the connecting rod, to 
which motion is imparted by the beams, through the medium 
of the cross tail extending between the beams, and which by 
means of the crank turns the paddle shaft s. The eccentric 
which works the slide valve is placed upon the paddle shaft. 
It consists of a disc of metal encircled by a hoop, to which a rod 
is attached, and the disc is perforated with a hole for the shaft, 
not in the centre, but near one edge. When, therefore, the 
shaft revolves, carrying the eccentric with it, the rod attached 
to the encircling hoop receives a reciprocating motion, just as it 
would do if attached to a crank in the shaft. 

116. Q. — Will you describe the mode of starting the engine ? 

A. — I may first mention that when the engine is at rest, the 
connection between the eccentric and the slide valve is broken, 
by lifting the end of the eccentric rod out of a notch which 
engages a pin on the valve shaft, and the valve is at such times 
free to be moved by hand by a bar of iron, applied to a proper 
part of the valve gear for that purpose. This being so, the 
engineer, when he wishes to start the engine, first opens a small 
valve called the Mow through vahe^ which permits steam from 
the boiler to enter the engine both above and below the piston, 
and also to fill the condenser and air pump. This steam expels 
the air from the interior of the engine, and also any water 
which may have accumulated there ; and when this has been 
done, the blow through valve is shut, and a vacuum very soon 
forms within the engine, by the condensation of the steam. If 
now the slide valve be moved by hand, the steam from the 
boiler will be admitted on one side of the piston, while there is 
a vacuum on the other side, and the piston will, therefore, be 



60 THE OSCILLATING PADDLE ENGINE. 

moved in the desired direction. When the piston reaches the 
end of the stroke, the valve has to be moved in the reverse 
direction, when the piston will return, and after being moved 
thus by hand, once or twice, the comiection of the valve with 
the eccentric is to be restored by allowing the notch on the 
end of the eccentric rod to engage the pin on the valve lever, 
when the valve will be thereafter moved by the engine in the 
l^roper manner. It will, of course, be necessary, w^hen the 
engine begins to move, to open the injection cock a little, to 
enable water to enter for the condensation of the steam. In 
the most recent marine engines, a somewhat different mechan- 
ism from this is used for giving motion to the valves, but that 
mechanism will be afterwards described. 

117. Q. — Are all marine engines condensing engines ? 

A. — Nearly all of them are so ; but recently a number of 
gunboats have been constructed, with high pressure engines. 
In general, however, marine engines are low pressure or con- 
densing engines. 

118. Q. — Will you now describe the chief features of the 
oscillating j)addle marine engine ? 

A, — In the oscillating paddle marine engine, the arrange- 
ment of the paddle shaft and paddle wheels is the same as in 
the case already described, but the whole of the side levers, side 
rods, cross head, cross tail, and connecting rod are discarded. 
The cylinder is set immediately under the crank ; the top of 
the piston rod is connected immediately to the crank pin ; and, 
to enable the piston rod to accommodate itself to the movement 
of the crank, the cylinder is so constructed as to be susceptible 
of vibrating or oscillating upon two external axes or trunnions. 
These trunnions are generally placed about half way up on the 
si({^s of the cylinder ; and through one of them steam is re- 
ceived from the boiler, while through the other the steam 
escapes to the condenser. The air pump is usually worked by 
means of a crank in the shaft, which crank moves the air pump 
bucket up and down as the shaft revolves. 

119. Q, — Will you give an example of a paddle oscillatuig 
cnmie ? 



ENGINES OP THE HOLYHEAD PACKETS. 61 

A, — I will take as an example tlic oscillating engines con- 
structed by Messrs. Ravenhill & Salked, for the Holyhead 
Packets. Fig. 27 is a longitudinal section of this vessel, show- 
ing an engine and boiler ; and fig. 28 is a transverse section 
of one of the engines, showing also one of the wheels. There 
are two cylinders in this vessel, and one air pump, which lies in 
an inclined position, and is worked by a crank in the shaft 
which stretches between the cylinders, and which is called the 
intermediate shaft, A A, is one of the cylinders, b b the pis- 
ton rod, and c c the crank, p is the crank in the intermediate 
shaft, which works the air pump e. There are double eccen- 
trics fixed on the shaft, whereby the movement of the slide 
valves is regulated. The purpose of the double eccentrics is to 
enable an improved arrangement of valve gear to be employed, 
which is denominated the link motion^ and which will be de- 
scribed hereafter. 1 1 are the steam pipes leading to the steam 
trunnions K k, on which, and on the eduction trunnions con- 
nected with the pipe m, the cylinders oscillate. 

120. Q, — By what species of mechanism are the positions of 
the paddle floats of feathering wheels governed ? 

A. — The floats are supported by spurs projecting from the 
rim of the wheel, and they may be moved upon the points of 
the spurs, to which they are attached by pins, by means of short 
levers proceeding from the backs of the floats, and connected to 
rods which proceed towards the centre of the wheel. The cen- 
tre, however, to which these rods proceed is not concentric 
with the wheel, and the rods, therefore, are moved in and out 
as the wheel revolves, and impart a corresponding motion to 
the floats. In some feathering wheels the proper motion is 
given to the rods by means of an eccentric on the ship's side. 
The action of paddle wheels, whether radial or feathering, will 
be more fully described in the chapter on Steam Navigation. 



SCREW ENGINES. 

121. Q. — What are the principal varieties of screw engines ? 
A. — The engines employed for the propulsion of screw vessels 
4 



ENGINES FOR DEIYING THE SCREW. 63 

are divided into two great classes, — geared engines and direct 
acting engines ; and each of these classes again has many 
varieties. In screw vessels, the shaft on which the screw is set 
requires to revolve at a much greater velocity than is required 
in the case of the paddle shaft of a paddle vessel ; and in geared 
engines this necessary velocity of rotation is obtained by the 
intervention of toothed wheels, — the engines themselves moving 
with the usual velocity of paddle engines ; whereas in direct 
acting engines the required velocity of rotation is obtained by 
accelerating the speed of the engines, and which are connected 
immediately to the screw shaft. 

122. Q, — Will you describe some of the principal varieties 
of geared engines ? 

A. — A good many of the geared engines for screw vessels 
are made in the same manner as land engines, with a beam 
overhead, which by means of a connecting rod extending down- 
wards, gives motion to the crank shaft, on which are set the cog 
wheels which give motion to pinions on the screw shaft,— the 
teeth of the wheels being generally of wood and the teeth of 
the pinions of iron. There are usually several wheels on the 
crank shaft and several pinions on the screw shaft ; but the 
teeth of each do not run in the same line, but are set a little in 
advance of one another, so as to divide the thickness of the 
tooth into as many parts as there are independent wheels or 
pinions. By this arrangement the wheels work more smoothly 
than they would otherwise do. 

123. Q, — What other forms are there of geared screw en- 
gines? 

A. — In some cases the cylinders lie on their sides in the 
manner of the cylinders of a locomotive engine. In other cases 
vertical trunk engines are employed ; and in other cases vertical 
oscillating engines. 

124. Q. — Will you give an example of a geared vertical oscil- 
lating engine ? 

A. — The engines of a geared oscillating engine are similar to 
the paddle wheel engines (figs. 27 and 28), but the engines are 
placed lengthways of the ship, and instead of a paddle wheel 



64 ENGINES OF THE GEEAT BRITAIN STEAMER. 

on the main shaft, there is a geared wheel which connects with 
a pinion on the screw shaft. The engines of the Great Britain 
are made off the same patterns as the paddle engines constructed 
by Messrs. John Penn & Son, for H. M. S. Sphinx. The diame- 
ter of each cylinder is 82 J inches, the length of travel or stroke 
of the piston is 6 feet, and the nominal power is 500 horses. 
The Great Britain is of 3,500 tons burden, and her displacement 
at 16 feet draught of water is 2,970 tons. The diameter of the 
screw is 15^^ feet, length of screw in the line of the shaft, 3 feet 
2 inches, and the pitch of the screw, 19 feet. 

125. Q. — What do you mean by the pitch of the screw ? 
A.— A screw propeller may be supposed to be a short piece 

cut off a screw of large diameter like a spiral stair, and the 
pitch of a spiral stair is the vertical height from any given step 
to the step immediately overhead. 

126. Q. — What is the usual number of arms ? 

A. — Generally a screw has two arms, but sometimes it has 
three or more. The Great Britain had three arms or twisted 
blades resembling the vanes of a windmill. The multiple of 
the gearing in the Great Britain is 3 to 1, and there are 17^ 
square feet of heating surface in the boiler for each nominal 
horse power. The crank shaft being put into motion by the 
engine, carries round with it the great cog wheel, or aggrega- 
tion of cog wheels, affixed to its extremity ; and these wheels 
acting on suitable pinions on the screw shaft, cause the screw 
to make three revolutions for every revolution made by the 
engine. 

127. Q. — What are the principal varieties of direct acting 
screw engines ? 

A. — In some cases four engines have been employed instead 
of two, and the cylinders have been laid on their sides on each 
side of the screw shaft. This multiplication of engines, how- 
ever, introduces needless complication, and is now but little 
used. In other cases two inverted cylinders are set above the 
screw shaft on appropriate framing ; and connecting rods 
attached to the ends of the piston rods turn round cranks in 
the screw shaft. 



OUTLINE OF THE LOCOMOTIVE ENGINE. G5 

128. Q. — What is tlie kind of direct acting screw engine 
employed by Messrs. Penn. 

A. — It is a horizontal trunk engine. In this engine a 
round pipe called a trunk penetrates the piston, to which it is 
fixed, being in fact cast in one piece with it ; and the trunk also 
penetrates the top and bottom of the cylinder, through which 
it moves, and is made tight therein by means of stuffing boxes. 
The connecting rod is attached at one end to a pin fixed in the 
middle of the trunk, while the other end engages the crank in 
the usual manner. The air pump is set within the condenser, 
and is wrought by a rod which is fixed to the piston and de- 
rives its motion therefrom. The air pump is of that species 
which is called double-acting. The piston or bucket is formed 
without valves in it, but an inlet and outlet valve is fixed to 
each end of the pump, through the one of which the water is 
drawn into the pump barrel, and through the other of which it 
is expelled into the hot well. 



THE LOCOMOTIVE ENGINE. 

129. Q. — Will you describe the more important features of 
the locomotive engine ? 

A. — The locomotive employed to draw carriages upon rail- 
ways, consists of a cylindrical boiler filled with brass tubes, 
through which the hot air passes on its progress from the fur- 
nace to the chimney, and attached to the boiler are two hori- 
zontal cylinders fitted with pistons, valves, connecting rods, and 
other necessary apparatus to enable the power exerted by the 
pistons to turn round the cranked axle to which the driving 
wheels are attached. There are, therefore, two independent 
engines entering into the composition of a locomotive, the 
cranks of which are set at right angles with one another, so that 
when one crank is at its dead point, the other crank is in a posi- 
tion to act with its maximum efficacy. The driving wheels, 
which are fixed on the crank shaft and turn round with it, 
propel the locomotive forward on the rails by the mere adhe- 
sion of friction, and this is found sufficient not merely to move 



66 LOCOMOTIVES ALWAYS HIGH PRESSURE. 

the locomotive, but to draw a long train of carriages be- 
hind it. 

130. Q. — Are locomotive engines condensing or high pres- 
sure engines. 

A. — They are invariably high pressure engines, and it would 
be impossible, or at least highly inconvenient, to carry the water 
necessary for the purpose of condensation. The steam, there- 
fore, after it has urged the piston to the end of the stroke, 
escapes into the atmosphere. In locomotive engines the waste 
steam is always discharged into the chinmey through a vertical 
pipe, and by its rapid passage it greatly increases the intensity 
of the draught in the chimney, whereby a smaller fire grate 
suffices for the combustion of the fuel, and the evaporative 
power of the boiler is much increased. 

131. Q. — Can you give an example of a good locomotive 
engine of the usual form ? 

A. — To do this I will take the example of one of Hawthorn's 
locomotive engines with six wheels represented in ^g. 29 ; not 
one of the most modern construction now in use, nor yet one of 
the most antiquated, m is the cylinder, r the connecting rod, 
c c the eccentrics by which the slide valve is moved ; j j is the 
steam pipe by which the steam is conducted from the steam 
dome of the boiler to the cylinder. Near the smoke stack end 
of this pipe is a valve k or regulator moved by a handle p at 
the front of the boiler, and of which the purpose is to regulate 
the admission of the steam to the cylinder ; / is a safety valve 
kept closed by springs ; n is the eduction pipe, or, as it is com- 
monly termed in locomotives, the llast pipe, by which the 
steam, escaping from the cylinder after the stroke has been per- 
formed, is projected up the chimney h. The water in the boiler 
of course covers the tubes and also the top of the furnace or 
fire box. It will be understood that there are two engines in 
each locomotive, though, from the figure being given in section, 
only one engine can be shown. The cylinders of this engine 
are each 14 inches diameter ; the length of the stroke of the 
piston is 21 inches. There are two sets of driving wheels, 5 
feet diameter, with outside connections. 



HA^VTHOENS LOCOMOTIVE. 



67 




68 



EXAMPLES OF MODERN LOCOMOTIVES. 



132. Q. — What is the tender of a locomotive ? 

A, — It is a carriage attached to the locomotive, of which the 
purpose is to contain coke for feeding the furnace, and water 
for replenishing the boiler. 

133. Q. — Can you give examples of modern locomotives ? 
A, — The most recent locomotives resemble in their material 

features the locomotive represented in ^g. 29. I can, however, 
give examples of some of the most powerful engines of recent 



Fis. 30. 




construction. Fig. 30 represents Gooch's express engine, adapted 

Fig. 81. 




for the wide gauge of the Great Western Railway ; and fig. 31 



HEAVY ENGINES INJURIOUS TO THE RAILS. 69 

represents Crampton's express engine, adapted for the ordi- 
nary or narrow gauge railways. The cylinders of Gooch's en- 
gine are each 18 inches diameter, and 24 inches stroke; the 
driving wheels are 8 feet in diameter ; the fire grate contains 
21 square feet of area ; and the heating surface of the fire box is 
153 square feet. There are in all 305 tubes in the boiler, each 
of 2 inches diameter, giving a heating surface in the tubes of 
1799 square feet. The total heating surface, therefore, is 1952 
square feet. Mr. Gooch states that an engine of this class will 
evaporate from 300 to 360 cubic feet of water in the hour, and 
will convey a load of 236 tons at a speed of 40 miles an hour, 
or a load of 181 tons at a speed of 60 miles an hour. The 
weight of this engine empty is 31 tons ; of the tender 8^ tons ; 
and the total weight of the engine when loaded is 50 tons. 
In one of Crampton's locomotives, the Liverpool, with one set 
more of carrying wheels than the Qg., the cylinders are of 24 
inches diameter and 18 inches stroke ; the driving wheels are 
8 feet in diameter ; the fire grate contains 21J- square feet of 
area ; and the heating surface of the fire box is 154 square feet. 
There are in all 300 tubes in the boiler of 2,^^ inches external 
diameter, giving a surface in the tubes of 2136 square feet, and 
a total heating surface of 2290 square feet. The weight of this 
engine is stated to be 35 tons when ready to proceed on a jour- 
ney. Both engines were displayed at the Great Exhibition in 
1851, as examples of the most powerful locomotive engines then 
made. The weight of such engines is very injurious to the 
railway ; bending, crushing, and disturbing the rails, and try- 
ing very severely the whole of the railway works. No doubt 
the weight may be distributed upon a greater number of 
wheels, but if the weight resting on the driving wheels be much 
reduced, they will not have sufficient bite upon the rails to pro- 
pel the train without slipping. This, however, is only one of the 
evils which the demand for high rates of speed has produced. The 
width of the railway, or, as it is termed, the gauge of the rails, 
being in most of the railways in this kingdom limited to 4 feet 
8J inches, a corresponding limitation is imposed on the diame- 
ter of the boiler ; which in its turn restricts the number of the 



70 LOSS OF POWER FROM LONG TUBES. 

tubes which can be employed. As, however, the attainment oi 
a high rate of speed requires much power, and consequently 
much heating surface in the boiler, and as the number of tubes 
cannot be increased without reducing their diameter, it has 
become necessary, in the case of powerful engines, to employ 
tubes of a small diameter, and of a great length, to obtain the 
necessary quantity of heating surface ; and such tubes require 
a very strong draught in the chimney to make them effective. 
With a draught of the usual intensity the whole of the heat 
wiU be absorbed in the portion of the tube nearest the fire box, 
leaving that portion nearest the smoke box nothing to do but 
to transmit the smoke ; and with long tubes of small diameter, 
therefore, a very strong draught is indispensable. To obtain 
such a draught in locomotives, it is necessary to contract the 
mouth of the blast pipe, whereby the waste steam will be pro- 
jected into the chimney with greater force ; but this contrac- 
tion involves an increase of the pressure on the eduction side 
of the piston, and consequently causes a diminution in the 
power of the engine. Locomotives with small and long tubes, 
therefore, will require more coke to do the same work than 
locomotives in which larger and shorter tubes may be employed. 



CHAPTER 11. 

HEAT, COMBUSTION, AND STEAM. 



HEAT. 

• 134. Q. — What is meant by latent heat ? 
^, — By latent heat is meant the heat existing in bodies 
which is not discoverable by the touch or by the thermometer, 
but which .manifests its existence by producing a change of 
state. Heat is absorbed in the liquefaction of ice, and in the 
vaporization of water, yet the temperature does not rise during 
either process, and the heat absorbed is therefore said to become 
latent. The term is somewhat objectionable, as the effect 
proper to the absorption of heat has in each case been made 
visible ; and it would be as reasonable to call hot water latent 
steam. Latent heat, in the present acceptation of the term, 
means sensible liquefaction or vaporization ; but to produce 
these changes heat is as necessary as to produce the expansion 
of mercury in a thermometer tube, which is taken as the 
measure of temperature ; and it is hard to see on what ground 
heat can be said to be latent when its presence is made manifest 
by changes which only heat can effect. It is the temperature 
only that is latent, and latent temperature means sensible va- 
porization or liquefaction. 



72 EXPLANATION OF THE NATURE OF LATENT HEAT. 

135. Q.—Bnt when you talk of the latent heat of steam, 
what do you mean to express ? 

A. — I mean to express the heat consumed in accomplishing 
the vaporization compared with that necessary for producing 
the temperature. The latent heat of steam is usually reckoned 
at about 1000 degrees, by which it is meant that there is as 
much heat in any given weight of steam as would raise its con- 
stituent water 1000 degrees if the expansion of the water could 
be prevented, or as would raise 1000 times that quantity of 
water one degree. The boiling point of water, being 212 de- 
grees, is 180 degrees above the freezing point of water — the 
freezing point being 32 degrees ; so that it requires 1180 times 
as much heat to raise 1 lb. of water into steam, as to raise 1180 
lbs. of water one degree ; or it requires about as much heat to 
raise a pound of boiling water into steam, as would raise 5 J lbs. 
of water from the freezing to the boiling point; 5 J multiplied 
by 180 being 990 or 1000 nearly. 

136. Q, — When it is stated that the latent heat of steam is 
1000 degrees, it is only meant that this is a rough approxima- 
tion to the truth ? 

A. — Precisely so. The latent heat, in point of fact, is not 
uniform at all temperatures, neither is the total amount of heat 
the same at all temperatures. M. Eegnault has shown, by a 
very elaborate series of experiments on steam, which he has 
lately concluded, that the total heat in steam increases some- 
what with the pressure, and that the latent heat diminishes 
somewhat with the pressure. This will be made obvious by 
the following numbers : 



Pressure. 


Temperature. 


Total Heat 


Latent Heat. 


15 lbs. 


213-1° 


1178-9° 


965-8° 


50 


281-0 


1199-6 


918-6 


100 


327-8 


1213-9 


886-1 



If, then, steam of 100 lbs. be expanded down to steam of 15 
lbs., it will have 35 degrees of heat over that which is required 
for the maintenance of the vaporous state, or, in other words, it 
wiU be surcharged with heat. 

137. Q. — What do you understand by specific heat ? 



EXPLANATION OF THE NATURE OF SPECIFIC HEAT. 13 

A. — By Specific heat, I understand the relative quantities of 
heat in bodies at the same temperature, just as by specific 
gravity I understand the relative quantities of matter in bodies 
of the same bulk. Equal weights of quicksilver and water at 
the same temperature do not contain the same quantities of 
heat, any more than equal bulks of those liquids contain the 
same quantity of matter. The absolute quantity of heat in any 
body is not known ; but the relative heat of bodies at the same 
temperature, or in other words their specific heats, have been 
ascertained and arranged in tables, — the specific heat of water 
being taken as unity. 

138. Q. — In what way does the specific heat of a body 
enable the quantity of heat in it to be determined ? 

A. — If any body has only half the specific heat of water, then 
a pound of that body will, at any given temperature, have only 
half the heat in it that is in a pound of water at the same tem- 
perature. The specific heat of air is '2669, that of water being 
1 ; or it is 3 '75 times less than that of water. An amount of 
heat, therefore, which would raise a pound of water 1 degree 
would raise a pound of air 3*75 degrees. 

COMBUSTION. 

139. Q. — What is the nature of combustion ? 

A. — Combustion is nothing more than an energetic chemical 
combination, or, in other words, it is the mutual neutralization 
of opposing electricities. When coal is brought to a high tem- 
perature it acquires a strong aflinity for oxygen, and combination 
with oxygen will produce more than suflicient heat to maintain 
the original temperature ; so that part of the heat is rendered 
applicable to other purposes. 

140. Q. — Does air consist of oxygen ? 

A. — Air consists of oxygen and nitrogen mixed together in 
the proportion of 3*29 lbs. of nitrogen to 1 lb. of oxygen. 
Every pound of coal requires about 2*66 lbs. of oxygen for its 
saturation, and therefore for every pound of coal burned, 8*75 
pounds of nitrogen must pass through the fire, supposing all 



74 AIR REQUIRED FOR COMBUSTION. 

the oxygen to enter into combination. In practice, however, 
this perfection of combination does not exist ; from one-third to 
one-half of the oxygen will pass through the fire without enter- 
ino: into combination at all : so that from 16 to 18 lbs. of air 
are required for every pound of coal burned. 18 lbs. of air are 
about 240 cubic feet, which may be taken as the quantity of air 
required for the combustion of a pound of coal in practice. 

141. Q. — What are the constituents of coal ? 

A. — The chief constituent of coal is carbon or pure charcoal, 
which is associated in various proportions with volatile and 
earthy matters. English coal contains 80 to 90 per cent, of 
carbon, and from 8 to 18 per cent, of volatile and earthy mat- 
ters, but sometimes more than this. The volatile matters are 
hydrogen, nitrogen, oxygen, and sulphur. 

142. Q. — What is the difference between antliraci:e and 
bituminous coal ? 

A, — Anthracite consists almost entirely of carbon, having 
91 per cent, of carbon, with about 7 per cent, of volatile matter 
and 2 per cent, of ashes. Newcastle coal contains aboi.t S3 per 
cent, of carbon, 14 per cent, of volatile matter, and 3 per cent, 
of ashes. 

143. Q. — Will you recapitulate the steps by which you de- 
termine the quantity of air required for the combustion of coal ? 

A. — Looking to the quantity of oxygen required to unite 
chemically with the various constituents of the coal, we find for 
example that in 100 lbs. of anthracite coal, consisting of 91*44 
lbs. of carbon, and 3*46 lbs. of hydrogen, we shall for the 91*44 
lbs. of carbon require 243*84 lbs. of oxygen — since to saturate a 
pound of carbon by the formation of carbonic acid, requires 2| 
lbs. of oxygen. To saturate a pound of hydrogen in the forma- 
tion of water, requires 8 lbs. of oxygen ; hence 3*46 lbs. of hy- 
drogen will take 27*68 lbs. of oxygen for its saturation. If then 
we add 243*84 lbs. to 27*68 lbs. we have 271*52 lbs. of oxygen 
required for the combustion of 100 lbs. of coal. A given 
weight of air contains nearly 23*32 per cent of oxygen ; hence 
to obtain 271*52 lbs. of oxygen, we must have about four times 
that quantity of atmospheric air, or more accurately, 1164 lbs. 



EVAPORATIVE EFFICACY OF COAL. 75 

of air for the combustion of 100 lbs. of coal. A cubic foot of 
air at ordinary temperature weighs about "075 lbs. ; so that 100 
lbs. of coal require 15,524 cubic feet of air, or 1 lb. of coal re- 
quires about 155 cubic feet of air, supposing every atom of the 
oxygen to enter into combination. If, then, from one-third to 
one-half of the air passes unconsumed through the fire, an allow- 
ance of 240 cubic feet of air for each pound of coal will be a 
small enough allowance to answer the requirements of practice, 
and in some cases as much as 300 cubic feet will be required, — 
the difference depending mainly on the peculiar configuration 
of the furnace. 

144. Q, — Can you state the evaporative eflicacy of a pound 
of coal ? 

A. — The evaporative eflicacy of a pound of carbon has been 
found experimentally to be equivalent to that necessary to raise 
14,000 lbs. of water through 1 degree, or 14 lbs. of water through 
1000 degrees, supposing the whole heat generated to be ab- 
sorbed by the water. Now, if the water be raised into steam 
from a temperature of 60°, then 1118*9° of heat will have to be 
imparted to it to convert it into steam of 15 lbs. pressure per 
square inch. 14,000 -^ 1118'9 = 12512 lbs. will be the num- 
ber of pounds of water, therefore, which a pound of carbon can 
raise into steam of 15 lbs. pressure from a temperature of 60°. 
This, however, is a considerably larger result than can be ex- 
pected in practice. 

145. Q, — Then what is the result that may be expected in 
practice ? 

A. — The evaporative powers of different coals appear to be 
nearly proportional to the quantity of carbon in them ; and 
bituminous coal is, therefore, less efficacious than coal consist- 
ing chiefly of pure carbon. A pound of the best Welsh or an- 
thracite coal is capable of raising from 9^ to 10 lbs. of water 
from 212° into steam, whereas a pound of the best Newcastle is 
not capable of raising more than about 8J lbs. of water from 
212° into steam ; and inferior coals will not raise more than 6^ 
lbs. of water into steam. In America it has been found that 1 
lb. of the best coal is equal to 2^ lbs. of pine wood, or, in some 



76 PROPER METHOD OF FIRING FURNACES. 

cases to 3 lbs. ; and a pound of pine wood will not usually 
evaporate more than about 2^ lbs. of water, though, by careful 
management, it may be made to evaporate 4 J lbs. Turf will 
generate rather more steam than wood. Coke is equal or some- 
what superior to the best coal in evaporative effect. 

146. Q. — How much water will a pound of coal raise into 
steam in ordinary boilers ? 

A, — From 6 to 8 lbs. of water in the generality of land 
boilers of medium quality, the difference depending on* the 
kind of boiler, the kind of coal, and other circumstances.. Mr. 
Watt reckoned his boilers as capable of evaporating 1008 cubic 
feet of water with a bushel or 84 lbs. of Newcastle coal, which 
is equivalent to 7^ lbs. of water evaporated by 1 lb. of coal, and 
this may be taken as the performance of common land boilers 
at the present time. In some of the Cornish boilers, however, 
a pound of coal raises 11-8 lbs. of boiling water into steam, or 
a cwt. of coal evaporates about 21 cubic feet of water from 212°. 

147. Q, — What method of firing ordinary furnaces is the best ? 
A. — The coals should be broken up into small pieces, and 

sprinkled thinly and evenly over the fire a little at a time. The 
thickness of the stratum of coal upon the grate should depend 
upon the intensity of the draught : in ordinary land or marine 
boilers it should be thin, whereas in locomotive boilers it re- 
quires to be much thicker. If the stratum of coal be thick 
while the draught is sluggish, the carbonic acid resulting from 
combustion combines with an additional atom of carbon in 
passing through the fire, and is converted into carbonic oxide, 
which may l.^e defined to be invisible smoke, as it carries off a 
portion of the fuel : if, on the contrary, the stratum of coal be 
thin while the draught is very rapid, an injurious refrigeration 
is occasioned by the excess of air passing through the furnace. 
The fire should always be spread of uniform thickness over the 
bars of the grate, and should be without any holes or uncovered 
places, which greatly diminish the effect of the fuel by the 
refrigeratory action of the stream of cold air which enters 
thereby. A wood fire requires to be about 6 inches thicker 
than a coal one, and a turf fire requires to be 3 or 4 inches 



SLOW AND EAPID COMBUSTION. 11 

tliicker than a wood one, so that the furnace bars must be placed 
lower where wood or turf is burned, to enable the surface of the 
fire to be at the same distance from the bottom of the boiler. 

148. Q. — Is a slow or a rapid combustion the most benefi- 
cial ? 

A. — A slow combustion is found by experiment to give 
the best results as regards economy of fuel, and theory tells us 
that the largest advantage will necessarily be obtained where 
adequate time has been afforded for a complete combination of 
the constituent atoms of the combustible, and the supporter of 
combustion. In many of the cases, however, which occur in 
practice, a slow combustion is not attainable ; but the tenden- 
cies of slow combustion are both to save the fuel, and to burn 
the smoke. 

149. Q.—ls not the combustion in the furnaces of the Cor- 
nish boilers very, slow ? 

A. — ^Yes, very slow ; and there is in consequence very little 
smoke evolved. The coal used in Cornwall is Welsh coal, 
which evolves but little smoke, and is therefore more favorable 
for the success of a smokeless furnace ; but in the manufactur- 
ing districts, where the coal is more bituminous, it is found 
that smoke may be almost wholly prevented by careful firing 
and by the use of a large capacity of furnace. 

150. Q. — Do you consider slow combustion to be an ad- 
visable thing to practise in steam vessels ? 

A, — ^ISTo, I do not. When the combustion is slow, the heat 
in the furnaces and flues is less intense, and a larger amount of 
heating surface consequently becomes necessary to absorb the 
heat. In locomotives, where the heat of the furnace is very in- 
tense, there will be the same economy of fuel with an allowance 
of 5 or 6 square feet of surface to evaporate a cubic foot of 
water as in common marine boilers with 10 or 12. 

151. Q. — What is the method of consuming smoke pursued 
in the manufacturing districts ? 

A, — In Manchester, where some stringent regulations for the 
prevention of smoke have for some time been in force, it is 
found that the readiest way of burning the smoke is to have a 



78 METHODS EMPLOYED TO BURN THE SMOKE. 

very large proportion of furnace room, whereby slow combus- 
tion may be carried on. In some cases, too, a favourable result 
is arrived at by raising a ridge of coal across the furnace lying 
against the bridge, and of the same height : this ridge speedily 
becomes a mass of incandescent coke, Tvhich promotes the com- 
bustion of the smoke passing over it. 

152. Q. — Is the method of admitting a stream of air into 
• the flues to burn the smoke regarded favorably ? 

A. — No ; it is found to be productive of injury to the boiler 
by the violent alternations of temperature it occasions, as at 
some times cold air impinges on the iron of the boiler, and at 
other times flame, — just as there happens to be smoke or no 
smoke emitted by the furnace. Boilers, therefore, operating 
upon this principle, speedily become leaky, and are much worn 
by oxidation, so that, if the pressure is considerable, they are 
liable to explode. It is very difficult to apportion the quantity 
of air admitted, to the varying wants of the fire ; and as air 
may at some times be rushing in when there is no smoke to con- 
sume, a loss of heat, and an increased consumption of fuel may 
be the result of the arrangement ; and, indeed, such is the result 
in practice, though a carefully performed experiment usually 
demonstrates a saving in fuel of 10 or 12 per cent. 

153. Q. — What other plans have been contrived for obviat- 
ing the nuisance of smoke ? 

A. — They are too various for enumeration, but most of them 
either operate upon the principle of admitting air into the flues 
to accomplish the combustion of the uninflammable parts of the 
smoke, or seek to attain the same object by passing the smoke 
over or through the fire or other incandescent material. Some 
of the plans, indeed, profess to burn the inflammable gases aa 
they are evolved from the coal, without permitting the admix- 
ture of any of the uninflammable products of combustion which 
enter into the composition of smoke ; but this object has been 
Tery imperfectly fulfilled in any of the contrivances yet brought 
under the notice of the public, and in some cases these contri- 
vances have been found to create weightier evils than they pro- 
fessed to relieve. 



PRIDEAUX'S AND WATT's SMOKE-CONSUMING FURNACES. 79 

154. Q. — You refer, I suppose, to Mr. Charles Wye Wil- 
liams' Argand furnace ? 

A. — I cMefly refer to it, though I also comprehend all other 
schemes in which there is a continuous admission of air into the 
flues, with an intermittent generation of smoke. 

155. Q. — This is not so in Prideaux's furnace ? 

A, — No ; in that furnace the air is admitted only during a 
certain interval, or for so long, in fact, as there is smoke to be 
consumed. 

156. Q. — Will you explain the chief peculiarities of that, 
furnace ? 

A. — The whole peculiarity is in the furnace door. The front 
of the door consists of metal Venetians, which are opened when 
the top lever is lifted up, and shut when that lever descends to 
its lowest position. When the furnace door is opened to re- 
plenish the fire with coals, the top lever is raised up, and with 
it the piston of the small cylinder attached to the side of the 
furnace. The Venetians are thereby opened, and a stream of 
air enters the furnace, which, being heated in its passage among 
the numerous heated plates attached to the back of the furnace 
door, is in a favorable condition for efiecting the combustion of 
the inflammable parts of the smoke. The piston in the small 
cylinder gradually subsides and closes the Venetians ; and the 
rate of the subsidence of the piston may obviously be regulated 
by a cock, or, as in this case, a small screw valve, so that the 
Venetians shall just close when there is no more smoke to be 
consumed ; — the air or other fluid within the cylinder being 
forced out by the piston in its descent. 

157. Q. — Had Mr. Watt any method of consuming smoke ? 
A, — He tried various methods, but eventually fixed upon 

the method of coking the coal on a dead plate at the furnace 
door, before pushing it into the fire. That method is perfectly 
eflectual where the combustion is so slow that the requisite 
time for coking is allowed, and it is much preferable to any of 
the methods of admitting air at the bridge or elsewhere, to 
accomplish the combustion of the inflammable parts of the 
smoke. 



80 FUIINACE WITH KEVOLYING GRATE. 

158. Q. — What are the details of Mr. "Watt's arrangement as 
now employed ? 

A. — The fire bars and the dead plate are both set at a con- 
siderable inclination, to facilitate the advance of the fuel into 
the furnace. In Boulton and Watt's 30 horse power land boiler, 
the dead plate and the furnace bars are both about 4 feet long, 
and they are set at the angle of 30 degrees with the horizon. 

159. Q. — Is the use of the dead plate universally adopted in 
Boulton and Watt's land boilers ? 

A. — It is generally adopted, but in some cases Boulton and 
Watt have substituted the plan of a revolving grate for con- 
suming the smoke, and the dead plate then becomes both super- 
fluous and inapplicable. In this contrivance the fire is replen- 
ished with coals by a self-acting mechanism. 

160. Q. — Will you explain the arrangement of the revolving 
grate ? 

A, — The fire grate is made like a round table capable of 
turning horizontally upon a centre ; a shower of coal is precipi- 
tated upon the grate through a slit in the boiler near the fur- 
nace mouth, and the smoke evolved from the coal dropped at 
the front part of the fire is consumed by passing over the incan- 
descent fuel at the back part, from which all the smoke must 
have been expelled in the revolution of the grate before it can 
have reached that position. 

161. Q. — Is a furnace with a revolving grate applicable to a 
steam vessel ? 

A. — I see nothing to prevent its application. But the ar- 
rangement of the boiler would perhaps require to be changed, 
and it might be preferable to combine its use with the employ- 
ment of vertical tubes, for the transmission of the smoke. The 
introduction of any efiectual automatic contrivance for feeding 
the fire in steam vessels, would bring about an important 
economy, at the same time that it would give the assurance of 
the work being better done. It is very difficult to fire furnaces 
by hand efiectually at sea, especially in rough weather and in 
tropical climates ; whereas machinery would be unafiected by 
any such disturbing causes, and would perform with little ex' 
pense the work of many men. 



JUCKES' AND MAUDSLAy's SELF-FEEDING FURNACES. 81 

162. Q. — The introduction of some mechanical method of 
feeding the fire with coals would enable a double tier of fur- 
naces to be adopted in steam vessels without inconvenience ? 

A, — Yes, it would have at least that tendency ; and as the 
space available for area of grate is limited in a steam vessel by 
the width of the vessel, it would be a great convenience if a 
double tier of furnaces could be employed without a diminished 
effect. It appears to me, however, that the objection would 
still remain of the steam raised by the lower furnace being 
cooled and deadened by the air entering the ash-pit of the 
upper fire, for it would strike upon the metal of the ash-pit 
bottom. 

163. Q, — Have any other plans been devised for feeding the 
fire by self-acting means besides that of a revolving grate ? 

A. — Yes, many plans, but none of them, perhaps, are free 
from an objectionable complication. In some arrangements the 
bars are made like screws, which being turned round slowly, 
gradually carry forward the coal ; while in other arrangements 
the same object is sought to be attained by alternately lifting 
and depressing every second bar at the end nearest the mouth 
of the furnace. In Juckes' furnace, the fire bars are arranged 
in the manner of rows of endless chains working over a roller 
at the mouth of the furnace, and another roller at the farther 
end of the furnace. These rollers are put into slow revolution, 
and the coal which is deposited at the mouth of the furnace is 
gradually carried forward by the motion of the chains, which 
act like an endless web. The clinkers and ashes left after the 
combustion of the coal, are precipitated into the ash-pit, where 
the chain turns down over the roller at the extremity of the 
furnace. In Messrs. Maudslays' plan of a self-feeding furnace 
the fire bars are formed of round tubes, and are placed trans- 
versely across the furnace. The ends of the bars gear into end- 
less screws running the whole length of the furnace, whereby 
motion is given to the bars, and the coal is thus carried gradu- 
ally forward. It is very doubtful whether any of these contri- 
vances satisfy all the conditions required in a plan for feeding 
furnaces of the ordinary form by self-acting means, but the prob- 



82 EXPERIMENTS ON THE ELASTIC FORCE OF STEAM. 

lem of providing a suitable contrivance, does not seem difficult 
of accomplishment, and will no doubt be effected under ade- 
quate temptation. 

164. Q. — Have not many plans been already contrived 
wbicb consume the smoke of furnaces very effectually ? 

A. — Yes, many plans ; and besides those already mentioned 
there are Hall's, Coupland's, Godson's, Kobinson's, Stevens's, 
Hazeldine's, Inche's, Bristow and Attwood's, and a great num- 
ber of others. One plan, which promises well, consists in 
making the flame descend through the fire bars, and the fire 
bars are formed of tubes set on an incline and filled with water, 
which water will circulate with a rapidity proportionate to the 
intensity of the heat. After all, however, the best remedy for 
smoke appears to consist in removing from it those portions 
which form the smoke before the coal is brought into use. 
Many valuable products may be got from the coal by subjecting 
it to this treatment ; and the residuum will be more valuable 
than before for the production of steam. 

STEAM. 

165. Q. — Have experiments been made to determine the 
elasticity of steam at different temperatures ? 

A. — Yes ; very careful experiments. The following rule 
expresses the results obtained by Mr. Southern : — To the given 
temperature in degrees of Fahrenheit add 51-3 degrees ; from 
the logarithm of the sum, subtract the logarithm of 135*767, 
which is 2*1327940 ; multiply the remainder by 5*13, and to the 
natural number answering to the sum, add the constant fraction 
•1, which will give the elastic force in inches of mercury. If 
the elastic force be known, and it is wanted to determine the 
corresponding temperature, the rule must be modified thus : — 
From the elastic force, in inches of mercury, subtract the deci- 
mal '1, divide the logarithm of the remainder by 5*13, and to 
the quotient add the logarithm 2*1327940; find the natural 
number answering to the sum, and subtract therefrom the con- 
stant 51*3 ; the remainder will be the temperature sought. The 



REGNAULT's experiments ok STEA3I. . 83 

Frencli Academy, and the Franklin Institute, have repeated Mr. 
Southern's experiments on a larger scale ; the results obtained 
by them are not widely different, and are perhaps nearer the 
truth, but Mr. Southern's results are generally adopted by engi- 
neers, as sufficiently accurate for practical purposes. 

166. Q. — Have not some superior experiments upon this sub- 
ject been lately made in France ? 

A, — Yes, the experiments of M. Regnault upon this subject 
have been very elaborate and very carefully conducted, and the 
results are probably more accurate than have been heretofore 
obtained. Nevertheless, it is questionable how far it is advisa- 
ble to disturb the rules of Watt and Southern, with which 
the practice of engineers is very much identified, for the sake 
of emendations which are not of such magnitude as to influence 
materially the practical result. M. Regnault has shown that 
the total amount of heat, existing in a given weight of steam, 
increases slightly with the pressure, so that the sum of the 
latent and sensible heats do not form a constant quantity. 
Thus, in steam of the atmospheric pressure, or with 14*7 lbs. 
upon the square inch, the sensible heat of the steam is 212 de- 
grees, the latent heat 966*6 degrees, and the sum of the latent 
and sensible heats 1178-6 degrees ; w^hereas in steam of 90 
pounds upon the square inch the sensible heat is 320*2 degrees, 
the latent heat 891*4 degrees, and the sum of the latent and sen- 
sible heats 1211*0 degrees. There is, therefore, 33 degrees less 
of heat in any given weight of water, raised into steam of the 
atmospheric pressure, than if raised into steam of 90 lbs.* pres- 
sure. 

167. Q. — What expansion does water undergo in its conver- 
sion into steam? 

A. — A cubic inch of water makes about a cubic foot of steam 
of the atmospheric pressure. 

168. Q. — And how much at a higher pressure ? 

A. — That depends upon what the pressure is. But the pro- 
portion is easily ascertained, for the pressure and the bulk of a 

* A table containing the results arrived at by M. Regnault is given in the Key. 



84 HIGH PRESSURE STEAM IS STEAM COMPRESSED, 

given quantity ot steam, as of air or any other elastic fluid, are 
always inversely proportional to one another. Thus if a cubic 
inch of water makes a cubic foot of steam, with the pressure of 
one atmosphere, it will make half a cubic foot with the pressure 
of two atmospheres, a third of a cubic foot with the pressure of 
three atmospheres, and so on in all other proportions. High 
pressure steam indeed is just low pressure steam forced into a 
less space, and the pressure will always be great in the propor- 
tion in which the space is contracted. 

1^9. Q. — If this be so, the quantity of heat in a given 
Vv^eight of steam must be nearly the same, whether the steam is 
high or low pressure ? 

A. — Yes ; the heat in steam is nearly a constant quantity, at 
all pressures, but not so precisely. Steam to which an addi- 
tional quantity of heat has been imparted after leaving the 
boiler, or as it is called " surcharged steam," comes under a 
different law, for the elasticity of such steam may be increased 
without any addition being made to its weight ; but surcharged 
steam is not at present employed for working engines, and it 
may therefore be considered in practice that a pound of steam 
contains very nearly the same quantity of heat at all pressures. 

170. Q. — Does not the quantity of heat in any body vary 
with the temperature ? 

A. — Other circumstances remaining the same the quantity 
of heat in a body increases with the temperatures. 

171. Q. — And is not high pressure stemn. hotter than low 
pressure steam ? 

A, — Yes, the temperature of steam rises with the pressure. 

172. Q. — How then comes it, that there is the same quantity 
of heat in the same weight of high and low pressure steam, 
when the high pressure steam has the highest temperature ? 

A. — Because although the temperature or sensible heat rises 
with the pressure, the latent heat becomes less in about the 
same proportion. And as has been already explained, the 
latent and sensible heats taken together make up nearly the 
same amount at all temperatures ; but the amount is somewhat 
greater at the higher temperatures. As a damp sponge becomes 



LAW OF EXPANSION OF SUECHARGED STEAM. 85 

wet when subjected to pressure, so warm vapor becomes hot 
when forced into less bulk, but in neither case does the quantity 
of moisture or the quantity of heat sustain any alteration. 
Common air becomes so hot by compression that tinder may be 
inflamed by it, as is seen in the instrument for producing in- 
stantaneous light by suddenly forcing air into a syringe. 

173. Q, — What law is followed by surcharged steam on the 
application of heat ? 

A. — The same as that followed by air, in which the incre- 
ments in volume are very nearly in the same proportion as the 
increments in temperature ; and the increment in volume for 
each degree of increased temperature is 4^0^^ P^^^ ^^ ^^^ 
volume at 32°. A volume of air which, at the temperature of 
32°, occupies 100 cubic feet, will at 212° fill a space of 136*73 
cubic feet. The volume which air or steam — out of contact 
with water — of a given temperature acquires by being heated 
^o a higher temperature, the pressure remaining the same, may 
be found by the following rule : — To each of the temperatures 
before and after expansion, add the constant number 458: 
divide the greater sum by the less, and multiply the quotient 
by the volume at the lower temperature ; the product will give 
the expanded volume. 

174. Q. — If the relative volumes of steam and water are 
known, is it possible to tell the quantity of water which should 
be supplied to a boiler, when the quantity of steam expended is 
specified ? 

A. — ^Yes ; at the atmospheric pressure, about a cubic inch of 
water has to be supplied to the boiler for every cubic foot of 
steam abstracted ; at other pressures, the relative bulk of water 
and steam may be determined as follows : — To the temperature 
of steam in degrees of Fahrenheit, add the constant number 
458, multiply the sum by 37*3, and divide the product by the 
elastic force of the steam in pounds per square inch ; the 
quotient will give the volume required. 

175. Q, — Will this rule give the proper dimensions of the 
pump for feeding the boiler with water ? 

A. — No ; it is necessary in practice that the feed pump 
5 



86 SIZE NECESSARY FOK THE FEED PUMP. 

should be able to supply the boiler with a much larger quantity 
of water than what is indicated by these proportions, from the 
risk of leaks, priming, or other disarrangements, and the feed 
pump is usually made capable of raising 3 J times the water 
evaporated by the boiler. About ^ro^^ ^^ the capacity of the 
cylinder answers very well for the capacity of the feed jDump 
in the case of low pressure engines, supposing the cylinder to 
be double acting, and the pump single acting ; but it is better 
to exceed this size. 

176. Q. — Is this rule for the size of the feed pump applicable 
to the case of high pressure engines ? 

A, — Clearly not ; for since a cylinder full of high pressure 
steam, contains more water than the same cylinder full of low 
pressure steam, the size of the feed must vary in the same pro- 
portion as the density of the steam. In all pumps a good deal 
of the effect is lost from the imperfect action of the valves ; and 
in engines travelling at a high rate of speed, in particular, a 
large part of the water is apt to return through the suction 
valve of the pump, especially if much lift be permitted to that 
valve. In steam vessels moreover, where the boiler is fed with 
salt water, and where a certain quantity of supersalted water 
has to be blown out of the boiler from time to time, to prevent 
the water from reaching too high a degree of concentration, the 
feed pump requires to be of additional size to supply the extra 
quantity of water thus rendered necessary. When the feed 
water is boiling or very hot, as in some engines is the case, the 
feed pump will not draw from a depth, and will altogether act 
less efficiently, s^o that an extra size of pump has to be provided 
in consequence. These and other considerations which might 
be mentioned, show the propriety of making the feed pump 
very much larger than theory requires. The proper proportions 
of pumps, however, forms part of a subsequent chapter. 



"^ RECEIVED ^^ 

CHAPTER m. 

EXPANSION OF STEAM AND ACTION OF THE VALVES. 



177. Q. — Wliat is meant by working engines expansively ? 
A, — Adjusting the valves, so that the steam is shut off from 

the cylinder before the end of the stroke, whereby the residue 
of the stroke is left to be completed by the expanding steam. 

178. Q. — And what is the benefit of that practice ? 

A, — It accomplishes an important saving of steam, or, what 
is the same thing, of fuel ; but it diminishes the power of the 
engine, while increasing the power of the steam. A larger 
engine will be required to do the same work, but the work will 
be done with a smaller consumption of fuel. If, for example, 
the steam be shut off when only half the stroke is completed, 
there will only be half the quantity of steam used. But there 
will be more than half the power exerted ; for although the 
pressure of the steam decreases after the supply entering from 
the boiler is shut off, yet it imparts, during its expansion, sorne 
power, and that power, it is clear, is obtained without any ex- 
penditure of steam or fuel whatever. 

179. Q. — What will be the pressure of the steam, under such 
circumstances, at the end of the stroke ? 

A. — If the steam be shut off at half stroke, the pressure of . 
the steam, reckoning the total pressure both below and above 



88 LAW OF EXPANSION AND COMPEESSION. 

the atmosphere, will just be one-half ^of what it was at the bC' 
ginning of the stroke. It is a well known law of pneumatics, 
that the pressure of elastic fluids varies inversely as the spaces 
into which they are expanded or compressed. For example, if 
a cubic foot of air of the atmospheric density be compressed 
into the compass of half a cubic foot, its elasticity will be in- 
creased from 15 lbs. on the square inch to 30 lbs. on the square 
inch ; whereas, if its volume be enlarged to two cubic feet, its 
elasticity will be reduced to 7^ lbs. on the square inch, being 
just half its original pressure. The same law holds in all other 
proportions, and with all other gases and vapors, provided 
their temperature remains unchanged ; and if the steam valve 
of an engine be closed, when the piston has descended through 
one-fourth of the stroke, the steam within the cylinder will, at 
the end of the stroke, just exert one-fourth of its initial 
pressure. 

180. Q. — Then by computing the varying pressure at a 
number of stages, the average or mean pressure throughout the 
stroke may*be approximately determined ? 

A. — Precisely so. Thus in the accompanying figure, (fig. 32), 
let E be a cylinder, j the piston, a the steam pipe, c the upper 
port,/ the lower port, d the steam pipe, prolonged to e the 
equilibrium valve, g the eduction valve, m the steam jacket, N the 
cylinder cover, o stuffing box, n piston rod, p cylinder bottom ; 
let the cylinder be supposed to be divided in the direction of 
its length into any number of equal parts, say twenty, and let • 
the diameter of the cylinder represent the pressure of the steam, 
which, for the sake of simplicity, we may take at 10 lbs., so 
that we may divide the cylinder, in the direction of its diame- 
ter, into ten equal parts. If now the piston be supposed to 
descend through five of the divisions, and the steam valve then 
be shut, the pressure at each subsequent position of the piston 
^\i\\ be represented by a series, computed according to the laws 
of pneumatics, and which, if the initial pressure be represented 
by 1, will give a pressure of '5 at the middle of the stroke, and 
•25 at the end of it. If this scries be set ofi" on the horizontal 
lines, it will mark out a hyperbolic curve — the area of the part 



LAW OF EXPAKSIO:^r OF STEAM. 



89 



exterior to wMcli represents the total efficacy of the stroke, and 
the interior area, therefore, represents the diminution in the 
power of a stroke, when the steam is cut off at one-fourth of the 



Fig. 32. 




Diagi*am showing law of expansion of steam in a cylinder 

descent. If the squares above the point, where the steam is cut 
off, be counted, they will be found to amount to 50 ; and if 
those beneath that point be counted or estimated, they will be 
found to amount to about 69. These squares are representative 
of the power exerted ; so that while an amount of power repre- 
sented by 50 has been obtained by the expenditure of a quarter 
of a cylinder full of steam, we get an amount of power repre- 



90 MODE OF COMPUTING BENEFIT OF EXPANSION. 

sented by 69, without any expenditure of steam at all, merely 
by permitting the steam first used to expand into four times its 
original volume. 

181. Q, — Then by working an engine expansively, the 
power of the steam is increased, but the power of the engine is 
diminished ? 

A. — Yes. The efficacy of a given quantity of steam is more 
than doubled by expandmg the steam four times, while the 
efficacy of each stroke is made nearly one-half less. And, there- 
fore, to carry out the expansive principle in practice, the cylin- 
der requires to be larger than usual, or the piston faster than 
usual, in the proportion in which the expansion is carried out. 
Every one who is acquainted with simple arithmetic, can com- 
pute the terminal pressure of steam in a cylinder, when he 
knows the initial pressure and the point at which the steam is 
cut off; and he can also find, by the same process, any pressure 
intermediate between the first and the last. By setting down 
these pressures in a table, and taking their mean, he can deter- 
mine the effect, with tolerable accuracy, of any particular 
measure of expansion. It is necessary to remark, that it is the 
total pressure of the steam that he must take ; not the pressure 
above the atmosphere, but the pressure above a perfect vacuum. 

182. Q. — Can you give any rule for ascertaining at one 
operation the amount of benefit derivable from expansion ? 

A. — Divide the length of stroke through which the steam 
expands, by the length of stroke performed with full pressure, 
which last call 1 ; the hyperbolic logarithm of the quotient is 
the increase of efficiency due to expansion. According to this 
rule it will be found, that if a given quantity of steam, the 
power of which working at full pressure is represented by 1, be 
admitted into a cylinder of such a size that its ingress is con- 
cluded when one-half the stroke has been performed, its efficacy 
will be raised by expansion to 1*69 ; if the admission of the 
steam be stopped at one-third of the stroke, the efficacy will be 
2-10 ; at one-fourth, 239 ; at one-fifth, 261 ; at one-sixth, 2*79 ; 
at one-seventh, 2*95 ; at one-eighth, 308. The expansion, how- 
ever, cannot be carried beneficially so far as one-eighth, unless 



DIFFERENT KIXDS OP SLIDE YALYES. 



91 



the pressure of the steam in the boiler be very considerable, on 
account of the inconvenient size of cylinder or speed of piston 
which would require to be adopted, the friction of the engine, 
and the resistance of vapor in the condenser, which all become 
relatively greater with a smaller urging force. 

183. Q. — Is this amount of benefit actually realized in prac- 
tice ? 

A. — Only in some cases. It appears to be indispensable to 
the realization of any large amount of benefit by expansion, j 
that the cylinder should be enclosed in a steam jacket, or should 
in some other way be effectually protected from refrigeration. 
In some engines not so protected, it has been found experimen- 
tally that less benefit was obtained from the fuel by working 
expansively than by working without expansion — the whole 
benefit due to expansion being more than counteracted by the 
increased refrigeration due to the larger surface of the cylinder 
required to develop the power. In locomotive engines, with 
outside cylinders, this condition of the advantageous use of ex- 
pansion has been made very conspicuous, as has also been the 
case in screw steamers with four cylinders, and in which the 
refrigerating surface of the cylinders was consequently large. 

184. Q. — The steam is admitted to and from 
the cylinder by means of a slide or sluice valve ? 

A, — ^Yes; and of the slide valve there are 
many varieties ; but the kinds most in use are the 
D valve, — so called from its resemblance to a 
half cylinder or D in its cross section — and the 
three ported valve, shown in ^g. 33, which con- 
sists of a brass or iron box set over the two ports 
or openings into the cylinder, and a central port 
which conducts away the steam to the atmosphere 
or condenser ; but the length of the box is so ad- 
justed that it can only cover one of the cylinder 
ports and the central or eduction poii; at the same 
time. The effect, therefore, of moving the valve 
up and down, as is done by the eccentric, is to 
establish a connection alternately between each cylinder port 




92 EXPLANATIOX OF THE NATUEE OF LEAD. 

and the central passage whereby the steam escapes ; and while 
the steam is escaping from beneath the piston, the position of 
the valve is such, that a free communication exists between the 
space above the piston and the steam in the boiler. The piston 
is thus urged alternately up and down — the valve so changing 
its position before the piston arrives at the end of the stroke, 
that the pressure is by that time thrown on the reverse-side of 
the piston, so as to urge it into motion in the opposite direction. 

185. Q, — Is the motion of the valve, then, the reverse of 
that of the piston ? 

A. — No. The valve does not move down when the piston 
moves down, nor does it move down when the piston moves 
up ; but it moves from its mid position, to the extremity of its 
throw, and back again to its mid position, while the piston makes 
an upward or downward movement, so that the motion is as it 
were at right angles to the motion of the piston ; or it is the same 
motion that the piston of another engine, the crank of which is 
set at right angles with that of the first engine, would acquire. 

186. Q. — Then in a steam vessel the valve of one engine 
may be worked from the piston of the other ? 

A. — ^Yes, It may ; or it may be worked from its own connect- 
ing rod ; and in the case of locomotive engines, this has some- 
times been done. 

187. Q. — What is meant by the lead of the valve ? 

A. — The amount of opening which the valve presents for 
the admission of the steam, when the piston is just beginning 
its stroke. It is found expedient that the valve should have 
opened a little to admit steam on the reverse side of the piston 
before the stroke terminates ; and the amount of this opening, 
which is given by turning the eccentric more or less round 
upon the shaft, is what is termed the lead. 

188. Q. — And what is meant by the lap of the valve ? 

A. — It is an elongation of the valve face to a certain extent 
over the port, whereby the port is closed sooner than would 
otherwise be the case. This extension is chiefly effected at that 
part of the valve where the steam is admitted, or upon the 
steam side of the valve, as the technical phrase is ; and the intent 



MODE OF COMPUTING EFFECTS OF LAP AND LEAD. 93 

of the extension is to close the steam passage before the end of 
the stroke, whereby the engine is made to operate to a certain 
extent expansively. In some cases, however, there is also a cer- 
tain amount of lap given to the escape or eduction side, to pre- 
vent the eduction from being performed too soon when the 
lead is great ; but in all cases there is far less lap on the eduction 
than on the steam side, very often there is none, and sometimes 
less than none, so that the valve is incapable of covering both 
the ports at once. 

189. Q. — What is the usual proportional length of stroke of 
the valve ? 

A. — The common stroke of the valve in rotative engines is 
twice the breadth or depth of the port, and the length of the 
valve face will then be just the breadth of the port when there 
is lap on neither the steam nor eduction side. Whatever lap 
is given, therefore, makes the valve face just so much longer. 
In some engines, however, the stroke of the valve is a good 
deal more than twice the breadth of the port ; and it is to the 
stroke of the valve that the amount of lap should properly be 
referred. 

190. Q, — Can you tell what amount of lap will accomplish 
any given amount of expansion ? 

A. — ^Yes, when the stroke of the valve is known. From the 
length of the stroke of the piston subtract that part of the 
stroke which is intended to be accomplished before the steam 
is cut off; divide the remainder by the length of the stroke of 
the piston, and extract the square root of the quotient, which 
multiply by half the stroke of the valve, and from the product 
take half the lead ; the remainder will be the lap required. 

191. Q. — Can you state how we may discover at what point 
of the stroke the eduction passage will be closed ? 

A, — To find how much before the end of the stroke the 
eduction passage will be closed : — ^to the lap on the steam side 
add the lead, and divide the sum by half the stroke of the 
valve ; find the arc whose sine is equal to the quotient, and add 
90° to it ; divide the la|5 on the eduction side by half the stroke 
of the valve, and find the arc whose cosine is equal to the 



94 ADVANTAGES OF LEAD IN SWIFT ENGINES. 

quotient ; subtract this arc from tlie one last obtained, and 
find tlie cosine of the remainder ; subtract this cosine from 2, 
and multiply the remainder by half the stroke of the piston ; 
the product is the distance of the piston from the end of the 
stroke when the eduction passage is closed. 

192. Q. — Can you explain how we may determine the dis- 
tance of the piston from the end of the stroke, before the steam 
urging it onward is allowed to escape ? 

A. — To find how far the piston is from the end of its stroke 
when the steam that is prox3elling it by expansion is allowed to 
escape to the atmosphere or condenser — to the lap on the steam 
side add the lead ; divide the sum by half the stroke of the 
valve, and find the arc whose sine is equal to the quotient ; find 
the arc whose sine is equal to the lap on the eduction side, 
divided by half the stroke of the valve ; add these two arcs 
together and subtract 90° ; find the cosine of the residue, sub- 
tract it from 1, and multiply the remainder by half the stroke 
of the piston ; the product is the distance of the piston from 
the end of its stroke when the steam that is propelling it is 
allowed to escape into the atmosphere or condenser. In using 
these rules, all the dimensions are to be taken in inches, and 
the answers will be found in inches also. 

193. Q. — Is it a benefit or a detriment to open the eduction 
passage before the end of the stroke ? 

A. — In engines working at a high rate of speed, such as lo- 
comotive engines, it is very important to open the exhaust pas- 
sage for the escape of the steam before the end of the stroke, 
as an injurious amount of back pressure is thus prevented. In 
the earlier locomotives a great loss of efiect was produced from 
inattention to this condition ; and when lap was applied to the 
valves to enable the steam to be worked expansively, it was 
found that a still greater benefit was collaterally obtained by 
the earlier escape of the steam from the eduction passages, and 
which was incidental to the application of lap to the valves. 
The average consumption of coke per mile was reduced by Mr. 
Woods from 40 lbs. per mile to 15 lbs.' per mile, chiefly by giv- 
ing a free outlet to the escaping steam. 



1 



EFFECTS OF WIRE DRAWING THE STEAM. 95 

194. Q, — To wliat extent can expansion be carried benefi- 
cially by means of lap ujpon the valve ? 

A. — To about one-third of the stroke ; that is, the valve 
may be made with so much lap, that the steam will be cut off 
when two thirds of the stroke have been performed, leaving 
the residue to be accomplished by the agency of the expanding 
steam ; but if more lap be put on than answers to this amount 
of expansion, a very distorted action of the valve will be pro- 
duced, which may impair the efficiency of the engine. If a fur- 
ther amount of expansion than this is wanted, it may be accom- 
plished by wire drawing the steam, or by so contracting the 
steam passage that the pressure within the cylinder must decline 
when the speed of the piston is accelerated, as it is about the 
middle of the stroke. 

195. Q^ — ^ill you explain how this result ensues ? 

^.— If the valve be so made as to shut off the steam by the 
time two thirds of the stroke have been performed, and the 
steam be at the same time throttled in the steam pipe, the full 
pressure of the steam within the cylinder cannot be maintained 
except near the beginning of the stroke where the piston travels 
slowly ; for, as the speed of the piston increases, the pressure 
necessarily subsides, until the piston approaches the other end 
of the cylinder, where the pressure would rise again but that 
the operation of the lap on the valve by this time has had the 
effect of closing the communication between the cylinder and 
steam pipe, so as to prevent more steam from entering. By 
throttling the steam, therefore, in the manner here indicated, 
the amount of expansion due to the lap may be doubled, so 
that an engine with lap enough upon the valve to cut off the 
steam at two-thirds of the stroke, may, by the aid of wire draw- 
ing, be virtually rendered capable of cutting off the steam at 
one-third of the stroke. 

196. Q. — Is this the usual way of cutting off the steam ? 

A. — Ko ; the usual way of cutting oft' the steam is by means 
of a separate valve, termed an expansion valve ; but such a 
device appears to be hardly necessary in ordinary engines. In 
the Cornish engines, where the steam is cut off in some cases at 



96 



APPARATUS OF EXPANSION VALVES. 



one-twelftli of the stroke, a separate valve for the admission of 
steam, other than that which permits its escape, is of course 
indispensable ; but in common rotative engines, which may 
realize expansive efficacy by throttling, a separate expansion 
valve does not ajppear to be required. 

197. Q. — That is, where much expansion is required, an ex- 
pansion valve is a proper appendage, but where not much is re- 
quired, a separate expansion valve may be dispensed with ? 

A. — Precisely so. The wire drawing of the steam causes a 
loss of part of its power, and the result will not be quite so ad- 
vantageous by throttling as by cutting off. But for moderate 
amounts of expansion it will suffice, provided there be lap upon 
the slide valve. 

198. Q, — Will you explain the structure or configuration of 
expansion apparatus of the usual Construction ? 

A. — The structure of expansion apparatus is very various ; 
but all the kinds operate either on the principle of giving such 
a motion to the slide valve as vn.ll enable it to cut off the steam, 
at the desired point, or on the principle of shutting off the 
steam by a separate valve in the steam pipe or valve casing. 
The first class of apparatus has not been found so manageable, 
and is not in extensive use, except in that form known as the 
link motion. Of the second class, the most simple probably is 

the application of a cam giving mo- 
tion to the throttle valve, or to a 
valve of the same construction, 
which either accurately fits the 
steam pipe, or which comes round 
to a face, which, however, it is re- 
strained from touching by a suita- 
ble construction of the cam. A kind 
of expansion valve, often employed 
in marine engines of low speed, is 
the kind used in the Cornish en- 
gines, and known as the equilibrium 
valve. This valve is represented in 
^g. 34. It consists substantially of 



Fig, 84 




MODE OF ALTERING RATE OF EXPANSION. 97 

an annulus or bulging cylinder of brass, with a steam-tight 
face both at its upper and lower edges, at which points it 
fits accurately upon a stationary seat. This annulus may be 
raised or lowered without being resisted by the pressure 
of the steam, and in rotative engines it is usually worked 
by a cam on the shaft. The expansion cam is put on the 
shaft in two pieces, w^hich are fastened to each other by 
means of four bolts passing through lugs, and is fixed 
to the shaft by keys. A roller at one end of a bell-crank lever, 
which is connected with the expansion valve, presses against 
the cam, so that the motion of the lever will work the valve. 
The roller is kept against the c"km by a weight on a lever at- 
tached to the same shaft, but a spring is necessary for high 
speeds. If the cam were concentric with the shaft, the lever 
which presses upon it would remain stationary, and also the ex- 
pansion valve ; but by the projection of the cam, the end of the 
lever receives a reciprocating motion, which is communicated 
to the valve. 

199. Q, — The cam then works the valve ? 

A, — Yes. The position of the projection of the cam deter- 
mines the point in relation to the stroke at which the valve is 
opened, and its circumferential length determines the length of 
the time during which the valve continues open. The time at 
which the valve should begin to open is the same under all cir- 
cumstances, but the duration of its opening varies with the 
amount of expansion desired. In order to obtain this variable 
extent of expansion, there are several jDrojections made upon 
the cam, each of which gives a different degree, or grade as it is 
usually called, of expansion. These grades all begin at the 
same point on the cam, but are of different lengths, so that they 
begin to move the lever at the same time, but differ in the time 
of returning it to its original position. 

200. Q. — How is the degree of expansion changed ? 

^.— The change of expansion is effected by moving the rol- 
ler on to the desired grade ; which is done by slipping the lever 
carrying the roller endways on the shaft or pin sustaining it. 

201. §.— Are such cams applicable in all cases ? 



98 Stephenson's apparatus. 

A. — In engines moving at a liigh rate of speed the roller 
will be thrown back from the cam by its momentum, unless it 
be kept against it by means of springs. In some cases I have 
employed a spring formed of a great number of discs of India 
rubber to keep the roller against the cam, but a few brass discs 
require to be interposed to prevent the India rubber discs from 
being worn in the central hole. 

202. Q. — May not the percussion incident to the action of 
a cam at a high speed, when the roller is not kept up to the 
face by springs, be obviated by giving a suitable configuration 
to the cam itself ? 

A. — It may at all events be reduced. The outline of the 
cam should be a parabola, so that the valve may be set in mo- 
tion precisely as a falling body would be ; but it will, neverthe- 
less, be necessary that the roller on which the cam presses 
should be forced upward by a spring rather than by a counter- 
weight, as there will thus be less inertia or momentum in the 
mass that has to be moved. 

203. Q. — An additional slide valve is sometimes used for 
cutting off the steam ? 

A, — Yes, very frequently ; and the slide valve is sometimes 
on the side or back of the valve casing, and sometimes on the 
back of the main or distributing valve, and moving with it. 

204. Q, — Are cams used in locomotive engines ? 

A, — In locomotive engines the use of cams is inadmissible, 
and other expedients are employed, of which those contrived by 
Stephenson and by Cabrey operate on the principle of accom- 
plishing the requisite variations of expansion by altering the 
throw of the slide valve. 

205. Q, — What is Stephenson's arrangement ? 

A, — Stephenson connects the ends of the forward and back- 
ward eccentric rods by a link with a curved slot in which a 
pin upon the end of the valve rod works. By moving this link 
so as to bring the forward eccentric rod in the same line with 
the valve rod, the valve receives the motion due to that eccen- 
tric ; whereas if the backward eccentric rod is brought in a line 
with the valve rod, the valve gets the motion proper for revers- 



STEPHENSON'S LINK MOTION. 



99 



ing, and if the link be so placed tliat the valve rod is midway 
between the two eccentric rods, the valve will remain nearly 
stationary. This arrangement, which is now employed exten- 
sively, is what is termed "the link motion." It is represented 
in the annexed figure, fig. 35, where e is the valve rod, which is 




attached by a pin to an open curved link susceptible of being 
moved up and down by the bell-crank lever/"/'', supported on 
the centre ^, and acting on the links/, while the valve rod e 
remains in the same horizontal plane ; d d' are the eccentric 
rods, and the link is represented in its lowest position. The 
dotted lines h' h" show the position of the eccentric rods when 



100 VARIOUS KINDS OF EXPANSION VALVES. 

the link is in its highest position, and I I' when in mid posi- 
tion. 

206. Q, — What is Cabrey's arrangement ? 

A. — Mr. -Cabrey makes his eccentric rod terminate in a pin ' 
which works into a straight slotted lever, furnished with jaws 
similar to the jaws on the eccentric rods of locomotives. By 
raising the pin oT the eccentric rod in this slot, the travel of 
the valve will be varied, and expansive action will be the result. 

207. Q. — What other forms of apparatus are there for work- 
ing steam expansively ? 

A, — They are too numerous for description here, but a few 
of them may be enumerated. Fenton seeks to accomplish the 
desired object by introducing a spiral feather on the crank axle, 
by moving the eccentric laterally against which the eccentric is 
partially turned round so as to cut oflf the steam at a different 
part of the stroke. Dodds seeks to attain the same end by cor- 
responding mechanical an^angements. Farcot, Edwards, and 
Lavagrian cut off the steam by the application of a supplemen- 
tary valve at the back of the ordinary valve, which sujoplemen- 
tary valve is moved by tappets fixed to the valve casing. Bod- 
mer, in 1841, and Meyer, in 1842, employed two slides or blocks 
fitted over apertures in the ordinary slide valve, and which 
blocks were approximated or set apart by a right and left 
handed screw passing through both * Hawthorn, in 1843, em- 



* In 1838 I patented an arrangement of expansion valve, consisting of two 
movable plates set upon the ordinary slide valve, and which might be drawn to- 
gether or asunder by means of a right and left handed screw passing through both 
plates. The valve spindle was hollow, and a prolongation of the screw passed up 
through it, and was armed on the top with a small wheel, by means of which the 
y)lates might be adjusted while the engine was at work. In 1839 I fitted an expan- 
sion valve in a steam vessel, consisting of two plates, connected by a rod, and 
moved by tappets up against the steam edges of the valve. In another steam ves- 
sel I fitted the same species of valve, but the motion was not derived from tappets, 
but from a moving part of the engine, though at the moderate speed at which 
these engines worked I found tappets to operate well and make little noise. In 
1837 I employed, as an expansion valve, a rectangular throttle valve, accurately 
fitting a bored out seat, in which it might be made to revolve, though it did not re- 
volve in working. This valve was moved by a pin in a pinion, making two revo- 
lutions for every revolution of the engine, and the configuration of the seat deter* 



EXPANi^ION BY THE LINK MOTION. 101 

ployed as an expansion valve a species of frame lying on the 
ordinary cylmder face upon the outside of the valve, and work- 
ing up against the steam side of the valve at each end so as to 
cut off the steam. In the same year Gonzenbach patented an 
arrangement which consists of an additional slide valve and 
valve casing placed on the back of the ordinary slide valve 
casing, and through this supplementary valve the steam must 
first pass. This supplementary valve is worked by a double 
ended lever, slotted at one end for the reception of a pin on 
the valve link, the position of which in the slot determines the 
throw of the supplementary valve, and the consequent degree 
of expansion. 

208. Q. — What is the arrangement of expansion valve used 
in the most approved modern engines ? 

A, — In modern engines, either marine or locomotive, it is 
found that if they are fitted with the link motion, as they 
nearly all are, a very good expansive action can be obtained by 
giving a suitable adjustment to it, without employing an ex- 
pansion valve at all. Diagrams taken from engines worked in 
this manner show a very excellent result, and most of the mod- 
ern engines trust for their expansive working to the link mo- 
tion and the throttle valve. 

rained the amount of the expansion. In 1855 I have again used expansion valves 
of this construction in engines making one hundred revolutions per minute, and 
with perfectly satisfactory results.— J. B. 



CHAPTER IV. 

MODES OF ESTIMATING THE POWER AND PERFORMANCE 
OF ENGINES AND BOILERS. 



HORSES POWER. 



209. Q. — What do you understand by a horse power ? 

A. — An amount of mechanical force that will raise 33,000 
lbs. one foot high in a minute. This standard was adopted by 
Mr. "Watt, as the average force exerted by the strongest London 
horses ; the object of his investigation being to enable him to 
determine the relation between the power of a certain size of 
engine and the power of a horse, so that when it was desired to 
supersede the use of horses by the erection of an engine, he 
might, from the number of horses employed, determine the 
size of engine that would be suitable for the work. 

310. Q, — Then when we talk of an engine of 200 horse 
power, it is meant that the impelling efficacy is equal to that 
of 200 horses, each lifting 33,000 lbs. one foot high in a 
minute? 

A. — No, not now ; such was the case in Watt's engines, but 
the capacity of cylinder answerable to a horse power has been 
increased by most engineers since his time, and the pressure on 
the piston has been increased also, so that what is now called a 



DEFINITION OF HORSE POWER. 103 

200 horse power engine exerts, almost in every case, a greater 
power than was exerted in Watt's time, and a horse power, in 
the popular sense of the term, has become a mere conventional 
unit for expressing a certain size of engine, without reference to 
the power exerted. 

211. Q. — Then each nominal horse power of a modern en- 
gine may raise much more than 33,000 lbs. one foot high in a 
minute ? 

A. — Yes; some raise 52,000 lbs., others 60,000 lbs., and 
others 66,000 lbs., one foot high in a minute by each nominal 
horse power. Some engines indeed work as high as five times 
above the nominal power, and therefore no comparison can be 
made between the performances of different engines, unless the 
power actually exerted be first discovered. 

212. Q, — How is the power actually exerted by engines as- 
certained ? 

^.— By means of an instrument called the indicator, which 
is a miniature cylinder and piston attached to the cylinder 
cover of the main engine, and which indicates, by the pressure 
exerted on a spring, the amount of pressure or vacuum existing 
within the cylinder. From this pressure, expressed in pounds 
per square inch, deduct a pound and a half of pressure for fric- 
tion, the loss of power in working the air pump, &c. ; multiply 
the area of the piston in square inches by this residual pressure, 
and by the motion of the piston, in feet per minute, and divide 
by 33,000 ; the quotient is the actual number of horses power 
of the engine. The same result is attained by squaring the 
diameter of the cylinder, multiplying by the pressure per square 
inch, as shown by the indicator, less a pound and a half, and 
by the motion of the piston, in feet per minute, and dividing 
by 42,017. 

213. Q. — How is the nominal power of an engine ascer- 
tained ? 

A. — Since the nominal power is a mere conventional expres- 
sion, it is clear that it must be determined by a merely conven- 
tional process. The nominal power of ordinary condensing en- 
gines may be ascertained by the following rule : multiply the 



104 DIFFERENCE BETWEEN ACTUAL AND NOMINAL. 

square of the diameter of the cylinder in inches, by the velocity 
of the piston in feet per minute, and divide the product by 
6,000 ; the quotient is the number of nominal horses power. In 
using this rule, however, it is necessary to adopt the speed of 
piston prescribed by Mr. Watt, which varies with the length 
of the stroke. The speed of piston with a 2 feet stroke is, ac- 
cording to his system, 160 per minute ; with a 2 ft. 6 in. stroke, 
170 ; 3 ft., 180 ; 3 ft. 6 in., 189 ; 4 ft., 200 ; 5 ft., 215 ; 6 ft., 228 ; 
7 ft., 245 ; 8 ft, 256 ft. 

214. Q. — Does not the speed of the piston increase with the 
length of the stroke ? 

A. — It does : the speed of the piston varies nearly as the 
cube root of the length of the stroke. 

215. Q. — And may not therefore some multiple of the cube 
root of the length of the stroke be substituted for the velocity 
of the piston in determining the nominal power ? 

A. — The substitution is quite practicable, and will accom- 
plish some simplification, as the speed of piston proper for the 
difierent lengths of stroke cannot always be remembered. The 
rule for the nominal power of condensing engines when thus 
arranged, will be as follows : multiply the square of the diame- 
ter of the cylinder in inches by the cube root of the stroke in 
feet, and divide the product by 47 ; the quotient is the number 
of nominal horses power of the engine, supposing it to be of 
the ordinary condensing description. This rule assumes the 
existence of a uniform effective pressure upon the piston of 7 lbs. 
per square inch ; Mr. Watt estimated the effective pressure upon 
the piston of his 4 horse power engines at 68 lbs. per square 
inch, and the pressure increased slightly with the power, and 
became 6*94 lbs. per square inch in engines of 100 horse power ; 
but it appears to be more convenient to take a uniform pressure 
of 7 lbs. for all powers. Small engines, indeed, are somewhat 
less effective in proportion than large ones, but the difference 
can be made up by slightly increasing the pressure in the 
boiler ; and small boilers will bear such an increase without 
inconvenience. 



POWER OF HIGH PRESSURE ENGINES. 105 

216. Q. — How do you ascertain the power of high pressure 
engines ? 

A. — The actual power is readily ascertained by the indica- 
tor, by the same process by which the actual power of low pres- 
sure engines is ascertained. The friction of a locomotive en- 
gine when unloaded is found by experiment to be about 1 lb. 
per square inch on the surface of the pistons, and the addition- 
al friction causied by any additional resistance is estimated at 
about '14 of that resistance ; but it will be a sufficiently near 
approximation to the power consumed by friction in high pres- 
sure engines, if we make a deduction of a pound and a half 
from the pressure on that account, as in the case of low pressure 
engines. High pressure engines, it is true, have no air pump to 
work ; but the deduction of a pound and a half of pressure is 
relatively a much smaller one where the pressure is high, than 
where it does not much exceed the pressure of the atmosphere. 
The rule, therefore, for the actual horse power of a high pressure 
engine will stand thus : square the diameter of the cylinder in 
inches, multiply by the pressure of the steam in the cylinder per 
square inch less 1^ lb., and by the speed of the piston in feet 
per minute, and divide by 42,017 ; the quotient is the actual 
horse power. 

217. Q. — But how do you ascertain the nominal horse 
power of high pressure engines ? 

A. — The nominal horse power of a high pressure engine has 
never been defined ; but it should obviously hold the same re- 
lation to the actual power as that which obtains in the case of 
condensing engines, so that an engine of a given nominal power 
may be capable of performing the same work, whether high 
pressure or condensing. This relation is maintained in the fol- 
lowing rule, which expresses the nominal horse power of high 
pressure engines : multiply the square of the diameter of the 
cylinder in inches by the cube root of the length of stroke in 
feet, and divide the product by 15*6. This rule gives the nom- 
inal power of a high pressure engine three times greater than 
that of a low pressure engine of the same dimensions ; the aver- 
age effective pressure being taken at 21 lbs. per square inch 



106 ARRA]^GEMENTS PROPER FOR HIGH SPEEDS. 

instead of 7 lbs., and the speed of the piston in feet per minute 
being in both rules 128 times the cube root of the length of 
stroke.* 

218. Q. — Is 128 times the cube root of the stroke in feet per 
minute the ordinary speed of all engines ? 

A. — Locomotive engines travel at a quicker speed — an inno- 
vation brought about not by any process of scientific deduction, 
but by the accidents and exigencies of railway transit. Most 
other engines, however, travel at about the speed of 128 times 
the cube root of the stroke in feet ; but some marine condensing 
engines of recent construction travel at as high a rate as 700 
feet per minute. To mitigate the shock of the air pump valves 
in cases in which a high speed has been desirable, as in the 
case of marine engines employed to diive the screw propeller 
without intermediate gearing, India rubber discs, resting on a 
perforated metal plate, are now generally adopted ; but the 
India rubber should be very thick, and the guards employed to 
keep the discs down should be of the same diameter as the 
discs themselves. 

219. Q, — Can you suggest any eligible method of enabling 
condensing engines to work satisfactorily at a high rate of speed ? 

A. — The most feasible way of enabling condensing engines 
to work satisfactorily at a high speed, appears to lie in the ap- 
plication of balance weights to the engine, so as to balance the 
momentum of its moving parts, and the engine must also be 
made very strong and rigid. It appears to be advisable to per- 
form the condensation partly in the air pump, instead of alto- 
gether in the condenser, as a better vacuum and a superior ac- 
tion of the air pump valves will thus be obtained. Engines 
constructed upon this plan may be driven at four times the 
speed of common engines, whereby an engine of large power 
may be purchased for a very moderate price, and be capable of 
being put into a very small compass ; while the motion, from 
being more equable, will be better adapted for most purposes 
for which a rotary motion is required. Even for pumping 

♦ Tables of the horse power of both high and low pressure engines are given 
in the Key. 



w 



ADMIRALTY EULE FOR HORSE POWER. 107 

mines and blowing iron furnaces, engines of tliis kind appear 
likely to come into use, for they are more suitable tban other 
engines for driving the centrifugal pump, which in many cases 
appears likely to supersede other kinds of pumps for lifting 
water ; and they are also conveniently applicable to the driving 
of fans, which, when so arranged that the air condensed by one 
fan is employed to feed another, and so on through a series of 
4 or 5, have succeeded in forcing air into a furnace with a pres- 
sure of 2i lbs. on the square inch, and with a far steadier flow 
than can be obtained by a blast engine with any conceivable 
kind of compensating apparatus. They are equally applicable 
if blast cylinders be employed. 

220. Q. — Then, if by this modification of the engine you 
enable it to work at four times the speed, you also enable it to 
exert four times the power ? 

A, — Yes; always supposing it to be fully supplied with 
steam. The nominal power of this new species of engine can 
readily be ascertained by taking into accoimt the speed of the 
piston, and this is taken into account by the Admiralty rule for 
power. 

221. Q. — What is the Admiralty rule for determining the 
power of an engine ? 

A. — Square the diameter of the cylinder in inches, which 
multiply by the speed of the piston in feet per minute, and 
divide by 6,000 ; the quotient is the power of the engine by the 
Admiralty rule.* 

222. Q. — The high speed engine does not require so heavy a 
fly wheel as common engines ? 

A. — No ; the fly wheel will be lighter, both by virtue of its 
greater velocity of rotation, and because the impulse communi- 
cated by the piston is less in amount and more frequently re- 
peated, so as to approach more nearly to the condition of a 
uniform pressure. 

* Examj^le.—^ ha,t is the power of an engine of 42 inches diameter, 8^ feet 
btroke, and making 85 strokes per minute ? The speed of the piston will be 7 (the 
length of a double stroke) x 85 = 595 feet per minute. Now 42 x 42:= 1,764 x 595 
= 1,049,580-:- 6,000 = 175 horses power. 



108 MEASURES OF ACTUAL POWER. 

223. Q. — Can nominal be transformed into actual horse 
power ? 

A. — No ; that is not possible in the case of common condens- 
ing engines. The actual power exerted by an engine cannot 
be deduced from its nominal power, neither can the nominal 
power be deduced from the power actually exerted, or from 
anything else than the dimensions of the cylinder. The actual 
horse power being a dynamical unit, and the nominal horse 
power a measure of capacity of the cylinder, are obviously incom- 
parable things. 

224. Q. — That is, the nominal power is a commercial unit by 
which engines are bought and sold, and the actual power a 
scientific unit by which the quality of their performance is de- 
termined ? 

A. — Yes; the nominal power is as much a commercial 
measure as a yard or a bushel, and is not a thing to be ascertained 
by any process of science, but to be fixed by authority in the 
same manner as other measures. The actual power, on the con- 
trary, is a mechanical force or dynamical efibrt capable of rais- 
ing a given weight through a given distance in a given time, 
and of which the amount is ascertainable by scientific investiga- 
tion. 

225. Q. — Is there any other measure of an actual horse 
power than 33,000 lbs. raised one foot high in the minute ? 

A. — There cannot be any different measure, but there are 
several equivalent measures. Thus the evaporation of a cubic 
foot of water in the hour, or the expenditure of 33 cubic feet of 
low pressure steam per minute, is reckoned equivalent to an 
acual horse power, or 528 cubic feet of water raised one foot 
hisch in the minute involves the same result. 



DUTY OF ENGINES AND BOILERS. 

226. Q. — What is meant by the duty of a engine ? 
A. — The work done in relation to the fuel consumed. 

227. Q. — And how is the duty ascertained ? 

A. — In ordinary mill or marine engines it can only be asccr- 



DUTY OF ENGINES AND BOILERS. 109 

tained by the indicator, as the load upon such engines is vari- 
able, and cannot readily be determined ; but in the case of 
engines pumping water, where the load is constant, the number 
of strokes performed by the engine will represent the work 
done, and the amount of work done by a given quantity of coal 
represents the duty. In Cornwall the duty of an engine is ex- 
pressed by the number of millions of pounds raised one foot 
high by a bushel, or 94 lbs. of Welsh coal. A bushel of New- 
castle coal will only weigh 84 lbs. ; and in comparing the duty 
of a Cornish engine with the performance of an engine in some 
locality where a different kind of coal is used, it is necessary to 
pay regard to such variations. 

228. Q. — Can you tell the duty of an engine when you know 
its consumption of coal per horse power per hour ? 

A. — Yes, if the power given be the actual, and not the nom- 
inal, power. Divide 166-32 by the number of pounds of coal 
consumed per actual horse power per hour ; the quotient is the 
duty in millions of pounds. If you already have the duty in 
millions of pounds, and wish to know the equivalent consump- 
tion in pounds per actual horse power per hour, divide 166-32 
by the duty in millions of pounds ; the quotient is the con- 
sumption per actual horse power per hour. The duty of a loco- 
motive engine is expressed by the weight of coke it consumes 
in transporting a ton through the distance of one mile upon a 
railway ; but this is a very imperfect method of representing 
the duty, as the tractive efficacy of a pound of coke becomes 
less as the speed of the locomotive becomes greater ; and the 
law of variation is not accurately known, 

229. Q . — What amount of power is generated in good en- 
gines of the ordinary kind by a given weight of coal ? 

A. — The duty of different kinds of engines varies very much, 
and there are also great differences in the performance of differ- 
ent engines of the same class. In ordinary rotative condensing 
engines of good construction, 10 lbs. of coal per nominal horse 
power per hour is a common consumption ; but such engines 
exert nearly twice their nominal power, so that the consump- 
tion por actual horse power per hour may be taken at from 5 to 



\ 



110 BENEFITS OF A SMALL FIRE GRATE. 

6 lbs. Engines working very expansively, however, attain an 
economy mucli superior to tMs. The average duty of the 
lumping engines in Cornwall is about 60,000,000 lbs. raised 1 
ft. high by a bushel of Welsh coals, which weighs 94 lbs. This 
is equivalent to a consumption of 3*1 lbs. of coal per actual 
horse power per hour ; but some engines reach a duty of above 
100,000,000, or 1*74 lbs. of coal per actual horse power per hour. 
Locomotives consume from 8 to 10 lbs. of coke in evaporating 
a cubic foot of water, and the evaporation of a cubic foot of 
water per hour may be set down as representing an actual horse 
power in locomotives as well as in condensing engines, if expan- 
sion be not employed. When the locomotive is worked expan- 
sively, however, there is of course a less consumption of water 
and fuel per horse power, or per ton per mile, than when the 
full pressure is used throughout the stroke ; and most locomo- 
tives now operate with as much expansion as can be con- 
veniently given by the slide valves. 

230. Q. — But is not the evaporative power of locomotives 
affected materially by the proportions of the boiler ? 

A. — Yes, but this may be said of all boilers ; but in locomo- 
tive boilers, perhaps, the effect of any misproportion becomes 
more speedily manifest. A high temperature of the fire box is 
found to be conducive to economy of fuel ; and this condition, 
in its turn, involves a small area of grate bars. The heating 
surface of locomotive boilers should be about 80 square feet for 
each square foot of grate bars, and upon each foot of grate bars 
about 1 cwt. of coke should be burnt in the hour. 

231. Q. — Probably the heat is more rapidly absorbed when 
the temperature of the furnace is high ? 

A. — That seems to be the explanation. The rapidity with 
^hich a hot body imparts heat to a colder, varies as the square 
of the difference of temperature ; so that if the temperature of 
the furnace be very high, the larger part of the heat passes into 
the water at the furnace, thereby leaving little to be transmitted 
by the tubes. If, on the contrary, the temperature of the fur- 
nace be low, a large part of the heat will pass into the tubes, 
and niore tube surface will be required to absorb it. About 16 



STEAM AND VACUUM GAUGES. Ill 

cubic feet of water should be evaporated by a locomotive boiler 
for each square foot of fire grate, wMch, with the proportion of 
heating surface already mentioned, leaves 5 square feet of heat- 
ing surface to evaporate a cubic foot of water in the hour. This 
is only about half the amount of surface usual in land and 
marine boilers per cubic foot evaporated, and its small amount 
is due altogether to the high temperature of the furnace, which, 
by the rapidity of transmission it causes, is tantamount to an 
additional amount of heating surface. 

232. Q. — You have stated that the steam and vacuum 
gauges are generally glass tubes, up which mercury is forced by 
the steam or sucked by the vacuum ? 

A, — ^Vacuum gauges are very often of this construction, but 
steam gauges more frequently consist of a small iron tube, bent 
like the letter U, and into which mercury is poured. The one 
end of this tube communicates with the boiler, and the other 
end with the atmosphere ; and when the pressure of the steam 
rises in the boiler, the mercury is forced down in the leg com- 
municating with the boiler and rises in the other leg, and the 
difference of level in the legs denotes the pressure of the steam. 
In this gauge a rise of the mercury one inch in the one leg in- \' 
volves a difference of the level between the two legs of two 1 
inches, and an inch of rise is, therefore, equivalent to two inches 
of mercury, or a pound of pressure. A small float of wood is 
placed in the open leg to show the rise or fall of the mercury, 
and this leg is surmounted by a brass scale, graduated in inches, 
to the marks of which the float points. 

233. Q. — What other kinds of steam and vacuum gauges are 
there ? 

A. — There are many other kinds ; but probably Bourdon's \ 
gauges are now in more extended use than any other, and their \ 
operation has been found to be satisfactory in practice. The 
principle of their action may be explained to be, that a thin 
elliptical metal tube, if bent into a ring, will seek to coil or 
uncoil itself if subjected to external or internal pressure, and to 
an extent proportional to the pressure applied. The end of the 
tube is sharpened into an index, and moves to an extent corre- 



112 



STRUCTURE OP THE INDICATOR. 



A 



Fl- S6. 



spondiiig to the pressure applied to the tube ; but in the more 
recent forms of this apparatus, a dial and a hand, like those of 
a clock, are employed, and the hand is moved round by a 
toothed sector connected to the tube, and which sector acts on 

a pinion attached to the 
hand. Mr. Shank, of Pais- 
ley, has lately introduced a 
form of steam gauge like a 
thermometer, with a flat- 
tened bulb ; and the press- 
ure of the steam, by com- 
pressing the bulb, causes the 
mercury to rise to a point 
proportional to the press- 
ure applied. 



THE INDICATOR. 

234. (?.— You have aU 
ready stated that the actual 
power of an engine is ascer- 
tained by an instrument 
called the indicator, which 
consists of a small cylinder 
with a piston moving 
against a spring, and com- 
pressing it to an extent an- 
swerable to the pressure of 
the steam. Will you ex- 
plain further the structure 
and mode of using that in- 
strument ? 

A. — The structure of the 
common form of indicator 
will be most readily appre- 
hended by a reference to fig. 
30, which is a M'Naught's 
]>arrel A, a piece of paper is 



E 


1 










t 




E_ 


IT 


r^\ 


r 












— 


e. 








C ^ 


iT 










IC 








; 


IT 








7~ 


IT 








■— 


:ir 










-K 








L.. . 


P^ 


P 

nmCQ > 


9 


1 


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Q. 




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indicator. Upon a movable 



EXPLANATION OF INDICATOR DIAGRAM. 113 

wound, the ends of which are secured by the slight brass clamps 
shown in the drawing. The barrel is supported by the bracket 
^, proceeding from the body of the indicator, and at the bottom 
of the barrel a watch spring is coiled with one end attached to 
the barrel and the other end to the bracket, so that when the 
barrel is drawn round by a string wound upon its lower end 
like a roller blind, the spring returns the barrel to its original 
position, when the strmg is relaxed. The string is attached to 
some suitable part of the engine, and at every stroke the string 
is drawn out, turning round the barrel, and the barrel is re- 
turned again by the spring on the return stroke. 

235. Q. — But in what way can these reciprocations of the 
barrel determine the power of the engine ? 

A. — They do not determine it of themselves, but are only 
part of the operation. In the inside of the cylinder c there is a 
small piston moving steam tight in a cylinder of which d is the 
piston rod, and e a spiral spring of steel, which the piston,- when 
forced upwards by the steam or sucked downwards by the 
vacuum, either compresses or extends ; / is a cock attached to 
the cylinder of the indicator, and which is screwed into the 
cylinder cover. It is obvious that, so soon as this cock is 
opened, the piston will be forced up when the space above the 
piston of the engine is opened to the boiler, and sucked down 
when that space is opened to the condenser — in each case to an 
extent proportionate to the pressure of the steam or the perfec- 
tion of the vacuum, the top of the piston c being open to the 
atmosphere. A pencil, p, with a knife hinge, is inserted into 
the piston rod at e, and the point of the pencil bears upon the 
surface of the paper wound upon the drum A. If the drum a 
did not revolve, this pencil would merely trace on the paper a 
vertical line ; but as the drum A moves round and back again 
every stroke of the engine, and as the pencil moves up and 
down again every stroke of the engine, the combined move- 
ments trace upon the paper a species of rectangle, which is 
called an indicator diagram ; and the nature of tliis diagram 
determines the nature of the engine's performance. 

236. $.— How does it do this ? 



114 INTERPRETATION OF INDICATOR DIAGRAM. 

-4. — It is clear that if the pencil was moved up instantaneous- 
ly to the top of its stroke, and was also moved down instan- 
taneously to the bottom of its stroke, and if it remained with- 
out fluctuation while at the top and bottom, the figure described 
by the pencil would be a perfect rectangle, of which the vertical 
height would represent the total pressure of the steam and 
vacuum, and therefore the total pressure urging the piston of 
the engine. But in practice the pencil will neither rise nor fall 
instantaneously, nor will it remain at a uniform height through- 
out the stroke. If the steam be worked expansively the press- 
ure will begin to fall so soon as the steam is cut off; and at the 
end of the stroke, when the steam comes to be discharged, the 
subsidence of pressure will not be instantaneous, but will oc- 
cupy an appreciable time. It is clear, therefore, that in no 
engine can the diagram described by an indicator be a complete 
rectangle ; but the more nearly it approaches to a rectangle, the 
larger will be the power produced at every stroke with any 
given pressure, and the area of the space included within the 
diagram will in every case accurately represent the power ex- 
erted by the engine during that stroke. 

237. Q. — And how is this area ascertained ? 

A. — It may be ascertained in various ways ; but the usual 
mode is to take the vertical height of the diagram at a number 
of equidistant points on a base line, and then to take the mean 
of these severaT heights as representative of the mean pressure 
actually urging the piston. Now if you have the pressure on 
the piston per square inch, and if you know the number of 
square inches in its area, and the velocity with which it moves 
in feet per minute, you have obviously the dynamical effort of 
the engine, or, in other words, its actual power. 

238. Q. — How is the base line you have referred to ob- 
tained ? 

A. — In proceeding to take an indicator diagram, the first 
thing to be done is to allow the barrel to make two or three 
reciprocations with the pencil resting against it, before opening 
the cock attached to the cylinder. There will thus be traced a 
horizontal line, which is called the atmospheric line, and in con- 



P V 



EXAMPLE OF INDICATOR DIAGRAM. 



115 



densing engines, a part of the diagram will be above and a part 
of it below this line ; whereas, in high pressure engines the 
whole of the diagram will be above this line. Upon this line 
the vertical ordinates may be set off at equal distances, or upon 
any base line parallel to it ; but the usual course is to erect the 
ordinates on the atmospheric line. 

239. Q, — Will you give an example of an indicator diagram ? 

A, — Fig. 37 is an indicator diagram taken from a low pres- 

Fig. 3T. 



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1 

1 




























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/ 


V 














/ 


\ 














/ 


\ 














.^^ 


-vn 









- 


' 


l====T 





sure engine, and the waving line a l c^ forming a sort of 
irregular parallelogram, is that which is described by the pen- 
cil. The atmospheric line is represented by the line o o. The 
scale at the side shows the pressure of the steam, which in this 
engine rose to about 9 lbs. per square inch, and the vacuum 
fell to 11 lbs. The steam begins to be cut off when about 
one-fourth of the stroke has been performed, and the pressure 
consequently falls. 

240. Q. — Is this species of indicator which you have just 
described applicable to locomotive engines ? 

A. — It is no doubt applicable under suitable conditions ; but 
another species of indicator has been applied by Mr. Gooch to 
locomotive engines, which presents several features of superiori- 
ty for such a purpose. 

This indicator has its cylinder placed horizontally ; and its 
piston compresses two elliptical springs ; a slide valve is sub- 
stituted for a cock, to open or close the communication with 
the engine. The top of the piston rod of this indicator is con- 



116 GAUGES AND OTDER INSTRUMENTS. 

nected to the short arm of a smaller lever, to the longer arm of 
which the pencil is attached, and the pencil has thus a consider- 
ably larger amount of motion than the piston ; but it moves in 
the arc of a circle instead of in a straight line. The pencil 
marks on a web of paper, which is unwound from one drum 
and wound on to another, so that a succession of diagrams are 
taken without the necessity of any intermediate manipulation. 

241. Q, — These diagrams being taken with a pencil moving 
in an arc, will be of a distorted form ? 

A. — They will not be of the usual Ibrm, but they may be 
easily translated into the usual form. It is undoubtedly pref- 
erable that the indicator should act immediately in the pro- 
duction of the final form of diagram. 

DYNAMOMETER, GAUGES, AND CATARACT. 

242. Q. — "What other gauges or instruments are there for 
telling the state, or regulating the power of an engine ? 

A. — There is the counter for telling the number of strokes 
the engine makes, and the dynamometer for ascertaining the 
tractive power of steam vessels or locomotives ; then there are 
the gauge cocks, and glass tubes, or floats, for telling the height 
of water in the boiler ; and in pumping engines there is the 
cataract for regulating the speed of the engine. 

243. Q, — ^Will you describe the mechanism of the counter ? 

A. — The counter consists of a train of wheel work, so con- 
trived that by every stroke of the engine an index hand is 
moved forward a certain space, whereby the number of strokes 
made by the engine in any given time is accurately recorded. 
In most cases the motion is communicated by means of a detent, 
— attached to some reciprocating part of the engine, — to a 
ratchet wheel which gives motion to the other wheels in its slow 
revolution ; but it is preferable to derive the motion from some 
revolving part of the engine by means of an endless screw, as 
where the ratchet is used the detent will sometimes fail to carry 
it round the proper distance. In the counter contrived by Mr. 
Adic, an endless screw works into the rim of two small wheels 
situated on the same axis, but one wheel having a tooth more 



THE DYNAMOMETER. 117 

than the other, whereby a differential motion is obtained ; and 
the difference in the velocity of the two wheels, or their motion 
upon one another, expresses the number of strokes performed. 
The endless screw is attached to some revolving part of the 
engine, whereby a rotatory motion is imparted to it ; and the 
wheels into which the screws work hang down from it like a 
pendulum, and are kept stationary by the action of gravity. 

244. Q. — What is the nature of the dynamometer ? 

A. — The dynamometer employed for ascertaining the trac- 
tion upon railways consists of two flat springs joined together at 
the ends by links, and the amount of separation of the springs 
at the centre indicates, by means of a suitable hand and dial, 
the force of traction. A cylinder of oil, with a small hole 
through its piston, is sometimes added to this instrument to 
prevent sudden fluctuations. In screw vessels the forward 
thrust of the screw is measured by a dynamometer constructed 
on the principle of a weighing machine, in which a small spring 
pressure at the index will balance a very great pressure where 
the thrust is employed ; and in each case the variations of pres- 
sure are recorded by a pencil on a sheet of paper, carried for- 
ward by suitable mechanism, whereby the mean thrust is easily 
ascertained. The tractive force of paddle wheel steamers is 
ascertained by a dynamometer fixed on shore, to which the 
floating vessel is attached by a rope. Sometimes the power of 
an engine is ascertained by a friction break dynamometer ap- 
plied to the shaft. 

245. Q. — What will determine the amount of thrust shown 
by the dynamometer ? 

A. — In locomotives and in paddle steamers it will be deter- 
mined by the force turning the wheels, and by the smallness of 
the diameter of the wheels ; for with small wheels the thrust 
will be greater than with large wheels. In screw vessels the 
thrust will be determined by the force turning round the screw, 
and by the smallness of the screw's pitch ; for with any given 
force of torsion a fine pitch of screw will give a greater thrust 
than a coarse pitch of screw, just as is the case when a screw 
works in a solid nut. 



118 GLASS GAUGES OF THE BOILER. 

246. Q, — Will you explain tlie use of the glass gauges affixed 
to the boiler ? 

A. — The glass gauges are tubes affixed to the fronts of 
boilers, by the aid of which the height of the water within the 
boilers is readily ascertainable, for the water will stand at the 
same height in the tube as in the boiler, with which there is a 
communication maintained both at the top and bottom of the 
tube by suitable stopcocks. The cocks connecting the glass 
tube with the boiler should always be so constructed that the 
tube may be blown through with the steam, to clear it of any 
internal concretion that may impair its transparency ; and the 
construction of the sockets in which the tube is inserted should 
be such, that^ even when there is steam in the boiler, a broken 
tube may be replaced with facility. 

247. Q. — What then are the gauge cocks ? 

A. — The gauge cocks are cocks penetrating the boiler at 
different heights, and which, when opened, tell whether it is 
water or steam that exists at the level at which they are respect- 
ively inserted. It is unsafe to trust to the glass gauges alto- 
gether as a means of ascertaining the water level, as sometimes 
they become choked, and it is necessary, therefore, to have 
gauge cocks in addition ; but if the boiler be short of steam, 
and a partial vacuum be produced within it, the glass gauges 
become of essential service, as the gauge cocks will not operate 
in such a case, for though opened, instead of steam and water 
escaping from them, the air will rush into the boiler. It is ex- 
pedient to carry a pipe from the lower end of the glass tube 
downward into the water of the boiler, and a pipe from the 
upper end upward into the steam in the boiler, so as to prevent 
the water from boiling down through the tube, as it might 
otherwise do, and prevent the level of the water from being 
ascertainable. The average level of water in the boiler should 
be above the centre of the tube ; and the lowest of the gauge 
cocks should always run water, and the highest should always 
blow steam. 

248. Q. — Is not a float sometimes employed to indicate the 
level of the water in the boiler ? 



I 



THE CATARACT. 



119 



A. — A float for telling the height of water in the boiler is 
employed only in the case of land boilers, and its action is like 
that of a buoy floating on the surface, which, by means of a 
light rod passing vertically through the boiler, shows at what 
height the water stands. The float is usually formed of stone 
or iron, and is so counterbalanced as to make its operation the 
same as if it were a buoy of timber ; and it is generally put in 
connection with the feed valve, so that in proportion as the 
float rises, the supply of feed water is diminished. The feed 
water in land boilers is admitted from a small open cistern, 
situated at the top of an upright or stand pipe set upon the 
boiler, and in which there is a column of water sufficiently high 
to balance the pressure of the steam. 

249. Q, — What is the cataract which is employed to regu- 
late the speed of pumping engines ? 

A, — The cataract consists of a small pump-plunger 5 and 
barrel, set in a cistern of water, the barrel being furnished on 

Fig. 38. 




the one side with a valve, c, opening inwards, through which 
the water obtains admission to the pump chamber from the 
cistern, and on the other by a plug, d^ through which, if the 



120 ACTION OF THE CATARACT. 

plunger be forced down, the water must pass out of the pump 
chamber. The engine in the upward stroke of the piston, 
which is accomplished by the preponderance of weight at the 
pump end of the beam, raises up the plunger of the cataract by 
means of a small rod, — the water entering readily through the 
valve already referred to ; and when the engine reaches the 
top of the stroke, it liberates the rod by which the plunger has 
been drawn up, and the plunger then descends by gravity, 
forcing out the water through the cock, the orifice of which has 
previously been adjusted, and the plunger in its descent opens 
the injection valve, which causes the engine to make a stroke. 

250. Q. — Suppose the cock of the cataract be shut ? 

A. — If the cock of the cataract be shut, it is clear that the 
plunger cannot descend at all, and as in that case the injection 
valve cannot be opened, the engine must stand still ; but if the 
cock be slightly opened, the plunger will descend slowly, the 
injection valve will slowly open, and the engine will make a 
gradual stroke as it obtains the water necessary for condensa- 
tion. The extent to which the cock is open, therefore, will regu- 
late the speed with which the engine works ; so that, by the 
use of the cataract, the speed of the engine may be varied to 
suit the variations in the quantity of water requiring to be lifted 
from the mine. In some cases an air cylinder, and in other 
cases an oil cylinder, is employed instead of the apparatus just 
described ; but the principle on which the whole of these con- 
trivances operate is identical, and the only difference is in the 
detail. 

251. Q. — You have now shown that the performance of an 
engme is determinable by the indicator ; but how do you deter- 
mine the power of the boiler ? 

A. — By the quantity of water it evaporates. There is, how- 
ever, no very convenient instrument for determining the quan- 
tity of water supplied to a boiler, and the consequence is that 
this element is seldom ascertained. 



CHAPTER V. 

PROPORTION OF BOILERS. 



HEATING AND FIRE GRATE SURFACE. 

252. Q. — What are the considerations which must chiefly be 
attended to in settling the proportions of boilers ? 

A. — In the first place there must be sufficient grate surface to .\ 
enable the quantity of coal requisite for the production of the \ 
steam to be conveniently burnt, taking into account the inten- 
sity of the draught ; and in the next place there must be a 
sufficient flue surface readily to absorb the heat thus produced, 
so that there may be no needless waste of heat by the chimney. 
The flues, moreover, must have such an area, and the chinmey 
must be of such dimensions, as will enable a suitable draught 
through the fire to be maintained ; and finally the boiler must 
be made capable of containing such supplies of water and steam 
as will obviate inconvenient fluctuations in the water level, and 
abate the risk of water being carried over into the engine with 
the steam. With all these conditions the boiler must be as 
light and compact as possible, and must be so contrived as to 
be capable of being cleaned and repaired with facility. 

253. Q. — Supposing, then, that you had to proportion a 
boiler, which should be capable of supplying steam sufficient 
to propel a steam vessel or railway train at a given speed, or to 
perform any other given work, how would you proceed ? 



122 MODE OF PROPOETIONING BOILERS. 

A, — I would first ascertain the resistance which had to be 
overcome, and the velocity with which it was necessary to 
overcome it. I should then be in a position to know what 
pressure and volume of steam w^ere required to overcome the re- 
sistance at the prescribed rate of motion ; and, finally, I should 
allow a sufficient heating and fire grate surface in the boiler 
according to the kind of boiler it was, to furnish the requisite 
quantity of steam, or, in other words, to evaporate the requisite 
quantity of water. 

254. C. — Will you state the amount of heating surface and 
grate surface necessary to evaporate a given quantity of water ? 

A, — The number of square feet of heating or flue surface, 
required to evaporate a cubic foot of water per hour, is about 
70 square feet in Cornish boilers, 8 to 11 square feet in land 
and marine boilers, and 5 or 6 square feet in locomotive boilers. 
The number of square feet of heating surface per square foot of 
fire grate, is from 13 to 15 square feet in w^agon boilers ; about 
40 square feet in Cornish boilers ; and from 50 to 90 square feet 
in locomotive boilers. About 80 square feet in locomotives is a 
very good proportion. 

255. Q. — What is the heating surface of boilers per horse 
power ? 

A. — About 9 square feet of flue and furnace surface per horse 
power is the usual proportion in wagon boilers, reckoning the 
total surface as effective surface, if the boilers be of a considera- 
ble size ; but in the case of small boilers the proportion is 
larger. The total heating surface of a two horse power wagon 
boiler is, according to Boulton and Watt's proportions, 30 
square feet, or 15 ft. per horse power ; whereas, in the case of 
a 45 horse power boiler the total heating surface is 438 square 
feet, or 9*6 ft. per horse power. In marine boilers nearly the 
same proportions obtain. The original boilers of the Great 
Western steamer, by Messrs. Maudslay, were proportioned with 
about 10 square feet of flue and furnace surface per horse power, 
reckoning the total amount as efi*ective ; but in the boilers of 
the Retribution, by the same makers, but of larger size, a some- 
what smaller proportion of heating surface was adopted. Boul- 



w^ 



PROPOETIONS OF MARINE BOILERS. 123 



ton and Watt have found that in their marine flue boilers, 9 
square feet of flue and/urnace surface are requisite to boil off a 
cubic foot of water per hour, which is the proportion of heating 
surface that is allowed in their land boilers per horse power ; 
but inasmuch as in most modern engines, and especially in 
marine engines, the nominal considerably exceeds the actual 
power, they allow 11 or 12 square feet of heating surface per 
nominal horse power in their marine boilers, and they reckon 
as effective heating surface the tops of the flues, and the whole 
of the sides of the flues, but not the bottoms. For their land 
engines they still retain Mr. Watt's standard of power, which 
makes the actual and the nominal power identical ; and an 
actual horse power is the equivalent of a cubic foot of water 
raised into steam every hour. 

256. Q. — What is the proper proportion of fire grate per 
horse power ? 

A. — Boulton and Watt allow 0*64 of a square foot area of 
grate bars per nominal horse power in their marine boilers, and 
a good effect arises from this proportion ; but sometimes so 
large an area of fire grate cannot be conveniently got, and the 
proportion of half a square foot per horse power, which is the 
proportion adopted in the original boiler of the Great Western, 
seems to answer very well in engines working with a moderate 
pressure, and with some expansion ; and this proportion is now 
very widely adopted. With this allowance, there will be 22 to 
24 square feet of heating surface per square foot of fire grate ; 
and if the consumption of fuel be taken at 6 lbs. per nominal 
horse power per hour, there will be about 12 lbs. of coal con- 
sumed per hour on each square foot of grate. The furnaces 
should not be more than 6 ft. long, as, if much longer than this, 
it will be impossible to work them properly for any considera- 
ble length of time, as they will become choked with clinker at 
the back ends. 

257. Q. — What quantity of fuel is usually consumed per 
hour on each square foot of fire grate ? 

A, — The quantity of fuel burned on each square foot of fire 
grate per hour, varies very much in different boilers ; in wagon 



124 SECTIONAL AREA OF BOILER FLUES. 

boilers it is from 10 to 13 lbs. ; in Cornisli boilers from 3^ to 4 
lbs. ; and in locomotive boilers from 80 to 150 lbs. ; but about 
1 cwt. per hour is a good proportion in locomotives, as has been 
already explained. 

CALOEIMETER AND VENT. 

258. Q. — In what manner are the proper sectional area and 
the proper capacity of the flue of a boiler determined ? 

A, — The proper collective area for the escape of the smoke 
and flame over the furnace bridges in marine boilers is 19 
square inches per nominal horse power, according to Boulton 
and Watt's practice, and for the sectional area of the flue they 
allow 18 square inches per horse power. The sectional area of 
the flue in square inches is what is termed the calorimeter of the 
boiler, and the calorimeter divided by the length of the flue in 
feet is what is termed the 'cent In marine flue boilers of good 
construction the vent varies between the limits of 20 and 25, 
according to the size of the boiler and other circumstances — the 
largest boilers having generally the largest vents ; and the calo- 
rimeter divided by the vent will give the length of the flue in 
feet. The flues of all flue boilers diminish in their calorimeter 
as they approach the chimney, as the smoke contracts in its 
volume in proportion as it parts with its heat. 

259. Q. — Is the method of determining the dimensions of a 
boiler flue, by a reference to its vent and calorimeter, the 
method generally pursued ? 

A. — It is Boulton and Watt's method ; but some very satis- 
factory boilers have been made by allowing a proportion of 0*6 
of a square foot of fire grate per nominal horse power, and 
making the sectional area of the flue at the largest part ^jth of 
the area of fire grate, and at the smallest part, where it enters 
the chimney, -Jj th of the area of the fire grate. These propor- 
tions are retained whether the boiler is flue or tubular, and 
from 14 to 16 square feet of tube surface is allowed per nominal 
horse power. 

260. Q, — Are the proportions of vent and calorimeter, taken 
by Boulton and Watt for marine flue boilers, applicable also to 
wagon and tubular boilers ? 



PROPORTIONS OF CALORIMETER AND VENT. 125 

A, — No. In wagon and tubular boilers very different pro- 
portions prevail, yet the proportions of every kind of boiler are 
determinable on the same general principle. In wagon boilers 
the proportion of the perimeter of the flue which is effective as 
heating surface, is to the total perimeter as 1 to 3, or, in some 
cases as 1 to 2*5 ; and with any given area of flue, therefore, the 
length of the flue must be from 3 to 2*5 times greater than 
would be necessary if the total surface were effective, else the 
requisite quantity of heating surface will not be obtained. If, 
then, the vent be the calorimeter, divided by the length, and 
the length be made 3 or 2*5 times greater, the vent must become 
3 or 2-5 times less ; and in wagon boilers accordingly, the vent 
varies from 8 to 11 instead of from 21 to 25, as in the case of 
marine flue boilers. In tubular marine boilers the calorimeter 
is usually made only about half the amount allowed by Boulton 
and Watt for marine flue boilers, or, in other words, the collect- 
ive sectional area of the tubes, for the transmission of the 
smoke, is from 8 to 9 square inches per nominal horse power. 
It is better, however, to make the sectional area larger than 
this, and to work the boiler with the damper suflficiently closed 
to prevent the smoke and flame from rushing exclusively 
tlirough a few of the tubes. 

261. §.— What are the ordinary dimensions of the flue in 
wagon boilers ? 

A. — In Boulton and Watt's 45 horse wagon boiler the area 
of flue is 18 square inches per horse power, but the area per 
horse power increases very rapidly as the size of the boiler 
becomes less, and amounts to about 80 square inches per horse 
power in a boiler of 2 horse power. Some such" increase is ob- 
viously inevitable, if a similar form of flue be retained in the 
larger and smaller powers, and at the same time the elongation 
of tlie flue in the same proportion as the increase of any other 
dimension is prevented ; but in the smaller class of wagon 
boilers the consideration of facility of cleaning the flues is also 
operative in inducing a large proportion of sectional area. 
Boulton and Watt's 2 horse power wagon boiler has 30 square 
feet of surface, and the flue is 18 inches high above the level of 



126 DEFICIENT BOILER POWER NOT UNUSUAL. 

tlie boiler bottom, by 9 inches wide; while their 12 horse 
wagon boiler has 118 square feet of heating surface, and the 
dimensions of the flue similarly measured are 36 inches by 13 
inches. The width of the smaller flue, if similarly proportioned 
to the larger one, would be 6| inches, instead of 9 inches, and, 
by assuming this dimension, we should have the same propor- 
tion of sectional area per square foot of heating surface in both 
boilers. The length of flue in the 2 horse boiler is 19*5 ft., and 
in the 12 horse boiler 39 ft., so that the length and height of 
the flue are increased in the same proportion. 

262. Q. — Will you give an example of the proportions of a 
* flue, in the case of a marine boiler ? 

A. — The Nile steamer, with engines of 110 horse power by 
Boulton and Watt, is supplied with steam by two boilers, which 
are, therefore, of 55 horses power each. The height of the flue 
winding within the boiler is 60 inches, and its mean width 16 i 
inches, making a sectional area or calorimeter of 990 square 
inches, or 18 square inches per horse power of the boiler. The 
length of the flue is 39 ft., making the vent 25, which is the 
vent proper for large boilers. In the Dee and Solway steamers, 
by Scott and Sinclair, the calorimeter is only 9*72 square inches 
per horse power ; in the Eagle, by Caird, 11-9 ; in the Thames 
and Medway, by Maudslay, 11 "34, and in a great number of 
other cases it does not rise above 12 square inches per horse 
power ; but the engines of most of these vessels are intended to 
operate to a certain extent expansively, and the boilers are less 
powerful in evaporating efficacy on that account. 

203. Q. — Then the chief difference in the proportions estab- 
lished by Boulton and Watt, and those followed by the other 
manufacturers you have mentioned is, that Boulton and Watt 
set a more powerful boiler to do the same work ? 

A. — That is the main difference. The proportion which one 
part of the boiler bears to another part is very similar in the 
cases cited, but the proportion of boiler relatively to the size of 
the engine varies very materially. Thus the calorimeter of each 
loiler of the Dee and Solway is 1290 square inches ; of the 
Eagle, 1548 square inches ; and of the Thames and Medway, 



VARIATIONS OF EVAPORATING POWER. 127 

1134 square inches ; and the length of flue is 57, 60, and 52 ft. 
in the boilers respectively, which makes the respective vents 
23J, 25, and 21. Taking then the boiler of the Eagle for com- 
parison with the boiler of the Nile, as it has the same vent, it 
will be seen that the proportions of the two are almost identi- 
cal, for 990 is to 1548 as 39 is to 60, nearly ; but Messrs. Boul- 
ton and Watt would not have set a boiler like that of the Eagle 
to do so much work. 

264. Q, — Then the evaporating power of the boiler varies 
as the sectional area of the flue ? 

A. — The evaporating power varies as the square root of the 
area of the flue, if the length of the flue remain the same ; but 
it varies as the area simply, if the length of the flue be increased 
in the same proportion as its other dimensions. The evaporat- 
ing power of a boiler is referable to the amount of its heating 
surface, and the amount of heating surface in any flue or tube 
is proportional to the product of the length of the tube and the 
square root of its sectional area, multiplied by a certain quantity 
that is constant for each particular form. But in similar tubes 
the length is proportional to the square root of the sectional 
area ; therefore, in similar tubes, the amount of heating surface 
is proportional to the sectional area. On this area also depends 
the quantity of hot air passing through the flue, supposing the 
intensity of the draught to remain unaffected, and the quantity 
of hot air or smoke passing through the flue should vary in the 
same ratio as the quantity of surface. 

265. Q. — A boiler, therefore, to exert four times the power, 
should have four times the extent of heating surface, and four 
times the sectional area of flue for the transmission of the 
smoke ? 

A. — Yes ; and if the same form of flue is to be retained, it 
should be of twice the diameter and twice the length ; or twice 
the height and width if rectangular, and twice the length. As 
then the diameter or square root of the area increases in the 
same ratio as the length, the square root of the area divided by 
the length ought to be a constant quantity in each type of 
boiler, in order that the same proportions of flue may be re- 



128 RELATIONS OF FLUE AND TUBULAR BOILERS. 

tained ; and in wagon boilers without an internal flue, the 
height in inches of the flue encircling the boiler divided by the 
length of the flue in feet will be 1 very nearly. Instead of the 
square root of the area, the effective perimeter, or outline of 
that part of the cross section of the flue which is effective in 
generating steam, may be taken ; and the effective perimeter 
divided by the length ought to be a constant quantity in simi- 
lar forms of flues and with the same velocity of draught, what- 
ever the size of the flue may be. 

266. Q. — Will this proportion alter if the form of the flue 
be changed ? 

A. — It is clear, that with any given area of flue, to increase 
the perimeter by adopting a different shape is tantamount to a 
diminution of the length of the flue ; and, if the perimeter be 
diminished, the length of the flue must at the same time be in- 
creased, else it will be impossible to obtain the necessary 
amount of heating surface. In Boulton and Watt's wagon 
boilers, the sectional area of the flue in square inches per square 
foot of heating surface is 5*4 in the two horse boiler ; in the 
three horse it is 4*74 ; in the four horse, 4*35 ; six horse, 3*75 ; 
eight horse, 4*33 ; ten horse, 3*96 ; twelve horse, 3*63 ; eighteen 
horse, 3*17 ; thirty horse, 2*52; and in the forty-five horse boiler, 
2*05 square inches. Taking the amount of heating surface in 
the 45 horse boiler at 9 square feet per horse power, we obtain 
18 square inches of sectional area of flue per horse power, which 
is also Boulton and Watt's proportion of sectional area for 
marine boilers with internal flues. 

267. Q. — If to increase the perimeter of a flue is virtually to 
diminish the length, then a tubular boiler where the perimeter 
is in effect greatly extended ought to have but a short length 
of tube ? 

A. — The flue of the Nile steamer if reduced to the cylindri- 
cal form would be 35^ inches in diameter to have the same 
area ; but it would then require to be made 47J feet long, to 
have the same amount of heating surface, excluding the bottom 
as non-effective. Supposing that with these proportions the 
heat is sufficiently extracted from the smoke, then every tube 



LIMIT OF LENGTH OP TUBES. 129 

of a tubular boiler in wbich the same draught existed ought to 
have very nearly the same proportions. 

268. Q. — But what are the best proportions of the parts of 
tubular boilers relatively with one another ? 

A, — The proper relative proportions of the parts of tubular 
boilers may easily be ascertained by a reference to the settled 
proportions of flue boilers ; for the same general principles are 
operative in both cases. In the Nile steamer each boiler of 55 
horse power has about 497 square feet of flue surface or 9 square 
feet per horse power, reckoning the total surface as efiective. 
The area of the flue, which is rectangular is 990 square inches, 
therefore the area is equal to that of a tube 35^ inches in 
diameter ; and such a tube, to have a heating surface of 497 
square feet, must be 53*4 feet or 640-8 inches in length. The 
length, therefore, of the tube, will be about 18 times its diameter, 
and with the same velocity of draught these proportions must 
obtain, whatever the absolute dimensions of the tube may be. 
With a calorimeter, therefore, of 18 square inches per horse 
power, the length of a tube 3 inches diameter must not exceed 
4 feet 6 inches, since the heat will be sufficiently extracted from 
the smoke in this length, if the smoke only travels at the velo- 
city due to a calorimeter of 18 square inches per horse power. 

269. Q. — Is this, then, the maximum length of flue which 
can be used in tubular boilers with advantage ? 

A. — By no means. The tubes of tubular boilers are almost 
always more than 4 feet 6 inches long, but then the calorimeter 
is almost always less than 18 square inches per horse power — 
generally about two thirds of this. Indeed, tubular boilers 
with a large calorimeter are not found to be so satisfactory as 
where the calorimeter is small, partly from the propensity of the 
smoke in such cases to pass through a few of the tubes instead 
of the whole of them, and partly from the deposit of soot which 
takes place when the draught is sluggish. It is a very con- 
fusing practice, however, to speak of nominal horse power in 
connection with boilers, since that is a quantity quite indeter- 
minate. 



130 EVAPORATION THE TEST OF EFFICIENCY. 



EYAPORATIYE POWER OF BOILEES. 

270. Q. — The main tMng after all in boilers is their evapora- 
tive powers ? 

A. — The proportions of tubular boilers, as of all boilers, 
should obviously have reference to the evaporation required, 
whereas the demand upon the boiler for steam is very often 
reckoned contingent upon the nominal horse power of the 
engine ; and as the nominal power of an engine is a convention- 
al quantity by no means in uniform proportion to the actual 
quantity of steam consumed, perplexing complications as to 
the proper proportions of boilers have in consequence sprung up, 
to which most of the failures in that department of engineering 
may be imputed. It is highly expedient, therefore, in planning 
boilers for any particular engine, to consider exclusively the 
actual power required to be produced, and to apportion the 
capabilities of the boiler accordingly. 

271. Q. — In other words you would recommend the inquiry 
to be restricted to the mode of evaporating a given number of 
cubic feet of water in the hour, instead of embracing the prob- 
lem how an engine of a given nominal power was to be supplied 
with steam ? 

A. — I would first, as I have already stated,' consider the ac- 
tual power required to be produced, and then fix the amount 
of expansion to be adopted. If the engine had to work up to 
three times its nominal power, as is now common in marine 
engines, I should either increase correspondingly the quantity 
of evaporating surface in the boiler, or adopt such an amount 
of expansion as would increase threefold the efficacy of the 
steam, or combine in a modified manner both of these arrange- 
ments. Eeckoning the evaporation of a cubic foot of water in 
the hour as equivalent to an actual horse power, and allowing a 
square yard or 9 square feet as the proper proportion of flue 
surface to evaporate a cubic foot of water in the hour, it is clear 
that I must either give 27 square feet of heating surface in the 
boiler to have a trebled power vv^ithout expansion, or I must 



i 



I 



RELATION OP EVAPORATION TO HORSE POWER. 131 



cut off the steam at one seventh of the stroke to obtain a three- 
fold power without increasing the quantity of heating surface. 
By cutting off the steam, however, at one third of the stroke, a 
heating surface of 13 J square feet will give a threefold power, 
and it will- usually be the most judicious course to carry the 
expansion as far as possible, and then to add the proportion of 
heating surface necessary to make good the deficiency still 
found to exist. 

272. Q. — But is it certain that a cubic foot of water evapo- 
rated in the hour is equivalent to an actual horse power ? 

A. — An actual horse power as fixed by Watt is 33,000 lbs. 
raised one foot high in the minute ; and in "Watt's 40 horse 
power engine, with a 31^ I'^tich cylinder, 7 feet stroke, and making 
17^ strokes a minute, the effective pressure is 6*92 lbs. on the 
square inch clear of all deductions. Now, as a horse power is 
33,000 lbs. raised one foot high, and as there are 6*92 lbs, on 
the square inch, it is clear that 38,000 divided by 6*92, or 4768 
square inches with 6*92 lbs. on each if lifted 1 foot or 12 inches 
high, will also be equal to a horse power. But 4768 square 
inches multiplied by 12 inches in height is 57224*4 cubic inches, 
or 38-1 cubic feet, and this is the quantity of steam which must 
be expended per minute to produce an actual horse power. 

273. Q. — But are 33 cubic feet of steam expended per 
minute equivalent to a cubic foot of water expended in the 
hour? 

A. — Not precisely, but nearly so. A cubic foot of water 
produces 1669 cubic feet of steam of the atmospheric density of 
15 lbs. per square inch, whereas a consumption of 33 cubic feet 
of steam in the minute is 1980 cubic feet in the hour. In 
Watt's engines about one tenth was reckoned as loss in filling 
the waste spaces at the top and bottom of the cylinder, making 
1872 cubic feet as the quantity consumed per hour without this 
waste ; and in modern engines the waste at the ends of the 
cylinder is inconsiderable. 

274. Q — What power was generated by a cubic foot of 
water in the case of the Albion Mill engines when working 
without expansion ? 



132 PROPORTIONS OF MODERN BOILERS. 



\ 



A. — In the Albion Mill engines when working without ex- 
pansion, it was found that 1 lb. of water in the shape of steai 
raised 28,489 lbs. 1 foot high. A cubic foot of water, therefore, 
or 62J lbs., if consumed in the hour, would raise 1780562'5 lbs. 
one foot high in the hour, or would raise 29,676 lbs. one foot 
high in a minute ; and if to this we add one tenth for waste at 
the ends of the cylinder, a waste which hardly exists in modern 
engines, we have 32,643 lbs. raised one foot high in the minute, 
or a horse power very nearly. In some cases the approximation 
appears still nearer. Thus, in a 40 horse engine working with- 
out expansion, Watt found that '674 feet of w^ater were evapo- 
rated from the boiler per minute, which is just a cubic foot per 
horse power per hour ; but it is not certain in this case that the 
nominal and actual power were precisely identical. It will be 
quite safe, however, to reckon an actual horse power as produ- 
cible by the evaporation of a cubic foot of water in the hour in 
the case of engines working without expansion ; and for boiling 
oflf this quantity in flue or wagon boilers, about 8 lbs. of coal 
will be required and 9 square feet of flue surface. 

MODERN MARINE AND LOCOMOTIVE BOILERS. 

275. Q. — These proportions appear chiefly to refer to old 
boilers. I wish you to state what are the proportions of modern 
flue and tubular marine boilers. 

A. — In modern marine boilers the area of fire grate is less 
than in Mr. Watt's original boilers, where it was one square foot 
to nine square feet of heating surface. The heat in the furnace 
is consequently more intense, and a somewhat less amount of 
surface sufl^ces to evaporate a cubic foot of water. In Boulton 
and Watt's modern flue boilers they allow for the evaporation 
of a cubic foot of water 8 square feet of heating surface, 70 
square inches of fire grate, 13 square inches sectional area of 
flues, 6 square inches sectional area of chimney, 14 square 
inches area over furnace bridges, ratio of area of flue to area of 
fire grate 1 to 5*4. To evaporate a cubic foot of water per hour 
in tubular boilers, the proportions are — heating surface 9 square 



EXAMPLES OF LOCOMOTIVE BOILERS. 



133 



feet, fire grate 70 square inches, sectional area of tubes 10 square 
inches, sectional area of back uptake 12 square inches, sectional 
area of front uptake 10 square inches, sectional area of chimney 
7 square inches, ratio of diameter of tube to length of tube ^^th 
to 5oth, cubical content of boiler exclusive of steam chest 6*5 
cubic feet, cubical content of steam chest 1*5 cubic feet. 

276. Q. — These proportions do not apply to locomotive 
boilers ? 

A. — Not at all. In locomotive boilers the draught is main- 
tained by the projection of the waste steam which escapes from 
the cylinders up the chimney, and the draught is much more 
powerful and the combustion much more rapid than in cases in 
which the combustion is maintained by the natural draught of 
a chimney, except indeed the chimney be of very unusual tem- 
perature and height. The proportions proper for locomotive 
boilers will be seen by the dimensions of a few locomotives of 
approved construction, which have been found to give satisfac- 
tory results in practice, and which are recorded in the follow- 
ing Table : 





NAxME OF ENGINK. 


Great 
Britain. 


Pallas. 


Snake. 


Sphinx. 


Diameter of cylinder 

Leno"th of stroke 


18 in. 
24 in. 
8 ft. 
53 in. 
63 in. 
63 in. 

29 

fin. 

305 

2 in. 

11 ft. 3 in. 

iin. 

U% in. 

17 in. 

5iin. 

21 sq. ft. 

11-4 sq.ft. 

5-46 -sq. ft. 

4 sq. i\. 
1-77 sq.ft. 
23-76 sq. in. 
1627 sq. ft. 


15 in. 
20 in. 
6 ft. 
55 in. 
42 in. 
52 in. 


14i in. 

21 in. 

6ift. 

4Uin. 

43iin. 

m in. 

82 

fin. 

181 

Uin. 

10 ft. 8i in. 

iin. 

1/, in. 

13 in. 

4| in. 

12-4 sq. ft. 

5-54 sq. ft. 

2-8 sq. ft. 

2 sq. ft. 

•921 sq. ft. 

14-18 sq. in. 

823 sq. ft. 


18 in. 
24 in. 
5 ft. 
44 in. 
39^ in. 
bbi in. 

16 

1 in. 

142 

2i in. 

14 ft. 3i in. 

H in. 

15iin. 

4f in. 
10 56 sq ft. 

5 sq. ft. 
2-92 sq. ft. 
204 sq. ft. 
1 -31 sq. ft. 
17-7 sq. m. 
864 8 sq ft. 


Diameter of driving wheel. . 

Inside length of fire box 

Inside width of fire box 

Height of fire box above bars 

Number of fire bars 

Thickness of fire bars 

Number of tubes 


If in. 

134 

2 in. 

10 ft. 6 in. 

|in. 

H in. 

15 in. 

4^ in. 
16-04 sq ft. 
4 03 sq. ft. 
2-40 sq. ft. 
1-64 sq.ft. 
1-23 sq.ft. 
16-8 sq. in. 
66S-7 sq. ft. 


Outside diameter of tubes. . . 
Length of tubes 


Space between tubes 

Inside diameter of ferules. . . 

Diameter of chimney 

Diameter of blast orifice .... 
Area of fire grate 


Area of air space of grate. . . 
Area of tubes 


Area through ferules 

Area uf chimney 


Area of blast orifice 

Heating surface of tubes.. . . 



134 OPERATION OF THE BLAST PIPE IN LOCOMOTIVES. 



THE BLAST IN LOCOMOTIVES. 

277. Q. — What is the amount of draught produced in loco- 
motive boilers in comparison with that existing in other boilers ? 

A. — A good chimney of a land engine will produce a degree 
of exhaustion equal to from 1^ to 2J inches of water. In loco- 
motive boilers the exhaustion*is in some cases equal to 12 or 13 
inches of water, but from 3 to 6 inches is a more common pro- 
portion. 

278. Q. — And what loroe of blast is necessary to produce 
this exhaustion ? 

A. — The amount varies in different engines, depending on 
the sectional area of the tubes and other circumstances. But 
on the average, it may be asserted that such a pressure of blast 
as will support an inch of mercury, will maintain sufficient ex- 
haustion in the smoke box to support an inch of water ; and 
this ratio holds whether the exhaustion is little or great. To 
produce an exhaustion in the smoke box, therefore, of 6 inches 
of water, the waste steam would require to be of sufficient 
pressure to support a column of 6 inches of mercury, which is 
equivalent to a pressure of 3 lbs. on the square inch. 

279. Q. — How is the force of the blast determined ? 

A. — By the amount of contraction given to the mouth of the 
blast pipe, which is a pipe which conducts the waste steam 
from the cylinders and debouches at the foot of the chimney. 
If a strong blast be required, the mouth of this pipe requires to 
be correspondingly contracted, but such contraction throws a 
back pressure on the piston, and it is desirable to obtain the 
necessary draught with as little contraction of the blast pipe as 
possible. The blast pipe is generally a breeches pipe of which 
the legs join just before reaching the chimney ; but it is better 
to join the two cylinders below, and to let a single pipe ascend 
to within 12 or 18 inches of the foot of the chimney. If made 
with too short a piece of pipe above the joining, the steam will 
be projected against each side of the chimney alternately, and 
the draught will be damaged and the chimney worn. The blast 



EXHAUSTIONS IN FIEE BOX AND SMOKE BOX. 135 

pipe should not be regularly tapered, but should be large in the 
body and gathered in at the mouth. 

280. Q. — Is a large and high chimney conducive to strength 
of draught in locomotives ? 

A. — It has not been found to be so. A chimney of three or 
four times its own diameter in height appears to answer ftlUy as 
well as a longer one ; and it was found that when in an engine 
with 17 inch cylinders a chimney of ISJ inches was substituted 
for a chimney of 17^ inches, a superior performance was the 
result. The chimney of a locomotive should have half the area 
of the tubes at the ferules, which is the most contracted part, 
and the blast orifice should have Jgth of the area of the chimney. 
The sectional area of the tubes through the ferules should be as 
large as possible. Tubes without ferules it is found pass one 
fourth more air, and tubes with ferules only at the smoke box 
end pass one tenth more air than when there are ferules at 
both ends. 

281. Q. — Is the exhaustion produced by the blast as great 
in the fire box as in the smoke box ? 

A. — Experiments have been made to determine this, and in 
few cases has it been found to be more than about half as great 
as ordinary speeds ; but much depends on the amount of con- 
traction in the tubes. In an experiment made with an engine 
having 147 tubes of If inches external diameter, and 13 feet 10 
inches long, and with a fire grate having an area of 9^ square 
feet, the exhaustion at all speeds was found to be three times 
greater in the smoke box than in the fire box. The exhaustion 
in the smoke box was generally equivalent to 12 inches of 
water, while in the fire box it was equivalent to only 4 inches 
of water ; showing that 4 inches were required to draw the 
air through the grate and 8 inches through the tubes. 

282. Q. — What will be the increase of evaporation in a loco- 
motive from a given increase of exhaustion ? 

A. — The rate of evaporation in a locomotive or any other 
boiler will vary as the quantity of air passing through the fire, 
and the quantity of air passing through the fire will vary nearly 
as the square root of the exhaustion. With four times the ex- 



136 MODES OF REGULATING THE DRAUGHT. 

haustion, therefore, there will be about twice the evaporation, 
and experiment shows that this theoretical law holds with 
tolerable accuracy in practice. 

283. Q. — But the same exhaustion will not be produced by 
a given strength of blast in all engines ? 

A?—l^o ; engines with contracted fire grates and an inade- 
quate sectional area of tubes, will require a stronger blast than 
engines of better proportions ; but in any given engine the re- 
lations between the blast exhaustion and evaporation hold 
which have been already defined. 

284. Q, — Is the intensity of the draught under easy regula- 
tion? 

A. — The intensity of the draught may easily be diminished 
by partially closing the damper in the chimney, and it may be 
increased by contracting the orifice of the blast. A variable 
blast pipe, the orifice of which may be enlarged or contracted 
at pleasure, has been much used. There are various devices for 
this purpose, but the best appears to be that adopted in Ste- 
phenson's engine, where a conical nozzle is moved up or down 
within the blast pipe, which is made somewhat larger in diame- 
ter than the base of the cone, but with a ring projecting inter- 
nally, against which the base of the cone abuts when the nozzle 
is pushed up. When the nozzle stands at the top of the pipe 
the whole of the steam has to pass through it, and the intensity 
of the blast is increased by the increased velocity thus given to 
the steam ; whereas when the nozzle is moved downward the 
steam escapes through the annular opening left between the 
nozzle and the pipe, as well as through the nozzle itself, and the 
intensity of the blast is diminished by the enlargement of the 
opening for the escape of the steam thus made available. 

285. Q, — What is the best diameter for the tubes of locomo- 
tive boilers ? 

A, — Bury's locomotive with 14 inch cylinders contains 93 
tubes of 2Jth inches external diameter, and 10 feet 6 inches 
long ; whereas Stephenson's locomotive with 15 inch cylinders 
contains 150 tubes of l|ths external diameter, 13 feet 6 inches 
long. In Stephenson's boiler, in order that the part of the 



i 



COMPARISON OF MARINE AND LOCOMOTIVE BOILERS. 137 

tubes next the chimney may be of any avail for the generation 
of steam, the draught has to be very intense, which in its turn 
involves a considerable expenditure of power ; and it is ques- 
tionable whether the increased expenditure of power upon the 
blast, in Stephenson's long tubed locomotives, is compensated 
by the increased generation of steam consequent upon the ex- 
tension of the heating surface. When the tubes are small in 
diameter they are apt to become partially choked with pieces 
of coke ; but an internal diameter of Ifths may be employed 
without inconvenience if the draught be of medium intensity. 

288. Q, — ^Will you illustrate the relation between the length 
and diameter of locomotive tubes by a comparison with the 
proportion of flues in flue boilers ? 

A. — In most locomotives the velocity of the draught is such 
that it would require very long tubes to extract the heat from 
the products of combustion, if the heat were transmitted 
through the metal of the tubes with only the same facility as 
through the iron of ordinary flue boilers. The Nile steamer, 
with engines of 110 nominal horses power each, and with two 
boilers having two independent flues in each, of such dimen- 
sions as to make each flue equivalent to 55 nominal horses 
power, works at 62 per cent, above the nominal power, so that 
the actual evaporative efficacy of each flue would be equivalent 
to 89 actual horses power, supposing the engines to operate 
without expansion ; but as the mean pressure in the cylinder is 
somewhat less than the initial pressure, the evaporative efficacy 
of each flue may be reckoned equivalent to 80 actual horses 
power. With this evaporative power there is a calorimeter of 
990 square inches, or 12*3 square inches per actual horse power ; 
whereas in Stephenson's locomotive with 150 tubes, if the eva- 
porative power be taken at 200 cubic feet of water in the hour, 
which is a large supposition, the engine will be equal to 200 
actual horses power. If the internal diameter of the tubes be 
taken at thirteen eighths of an inch, the calorimeter per actual 
horse power will only be 1*1136 square inches, or in other words 
the calorimeter in the locomotive boiler will be 11*11 times less 
than in the flue boiler for the same power, so that the draught 



138 PROPORTIONS OF CHIMNEYS. 

in the locomotive must be 11-11 times stronger, and the ratio 
of the length of the tube to its diameter 11*11 times greater 
than in the flue boiler, supposing the heat to be transmitted 
with only the same facility. The flue of the Nile would require 
to be 35| inches in diameter if made of the cylindrical form, 
and 47| feet long; the tubes of a locomotive if l|ths inch 
diameter would only require to be 22*19 inches long with the 
same velocity of draught ; but as the draught is 11*11 times 
faster than in a flue boiler, the tubes ought to be 246*558 inches, 
or about 20J feet long according to this proportion. In prac- 
tice, however, they are one third less than this, which reduces 
the heating surface from 9 to 6 square feet per actual horse 
power, and this length even is found to be inconvenient. It is 
greatly preferable therefore to increase the calorimeter, and 
diminish the intensity of the draught. 

BOILER CHIMNEYS. 

287. Q. — By what process do you ascertain the dimensions 
of the chimney of a land boiler ? 

A. — By a reference to the volume of air it is necessary in a 
given time to supply to the burning fuel, and to the velocity 
of motion produced by the rarefaction in the chimney ; for the 
area of the chimney requires to be such, that with the velocity 
due to that rarefaction, the quantity of air requisite for the 
combustion of the fuel shall pass through the furnace in the 
specified time. Thus if 200 cubic feet of air of the atmospheric 
density are required for the combustion of a pound of coal, — 
though 250 lbs. is nearer the quantity generally required, — and 
10 lbs. of coal per horse power per hour are consumed by an 
engine, then 2000 cubic feet of air must be supplied to the 
furnace per horse power per hour, and the area of the chimney 
must be such as to deliver this quantity at the increased bulk 
due to the high temperature of the chimney when moving with 
the velocity the rarefaction within the chimney occasions, and 
which, in small chimneys, is usually such as to support a column 
of half an inch of water. The velocity with which a denser 



m 



qp-- 



PBOPOETIONS OP CHIMNEYS. 139 

fluid flows into a rarer one is equal to the velocity a heavy body 
acquires in falling through a height equal to the difference of 
altitude of two columns of the heavier fluid of such heights as 
will produce the respective pressures ; and, therefore, when the 
difference of pressure or amount of rarefaction in the chimney 
is known, it is easy to tell the velocity of motion which ought 
to be produced by it. In practice, however, these theoretical 
results are not to be trusted, until they have received such 
modifications as will make them representative of the practice 
of the most experienced constructors ? 

288. §.— What then is the rule followed by the most ex- 
perienced constructors ? 

A. — Boulton and Watt's rule for the dimensions of the chim- 
ney of a land engine is as follows : — multiply the number of 
pounds of coal consumed under the boiler per hour by 12, and 
divide the product by the square root of the height of the 
chimney in feet ; the quotient is the area of the chimney in 
square inches in the smallest part. A factory chimney suitable 
for a 20 horse boiler is commonly made about 20 in. square, 
inside, and 80 ft. high ; and these dimensions are those which 
answer to a consumption of 15 lbs. of coal per horse power per 
hour, v/hich is a very common consumption in factory engines. 
If 15 lbs. of coal be consumed per horse power per hour, the 
total consumption per hour in a 20 horse boiler will be 300 lbs., 
and 300 multiplied by 12=3600, and divided by 9 (the square 
root of the height) =400, which is the area of the chimney in 
square inches. It will not answer well to increase the height of 
a chimney of this area to more than 40 or 50 yards, without also 
increasing the area, nor will it be of utility to increase the area 
much without also increasing the height. The quantity of coal 
consumed per hour in pounds, multiplied by 5, and divided by 
the square root of the height of the chimney, is the proper col- 
lective area of the openings between the bars of the grate for 
the admission of air to the fire. 

289. Q. — Is this rule applicable to the chimneys of steam 
vessels ? 

A, — In steam vessels Boulton and Watt have heretofore been 



140 PROPORTIONS OF STEAM ROOM. 

in the habit of allowing 8| square inches of area of chimney pei 
horse power, but they now allow 6 square inches to 7 square 
inches. In some steam vessels a steam blast like that of a loco- 
motive, but of a smaller volume, is used in the chimney, and 
many of the evils of a boiler deficient in draught may be reme- 
died by this expedient, but a steam blast in a low pressure en- 
gine occasions an obvious waste of steam ; it also makes an un- 
pleasant noise, and in steam vessels it frequently produces the 
inconvenience of carrying the smaller parts of the coal up the 
chimney, and scattering it over the deck among the passengers. 
It is advisable, therefore, to give a sufficient calorimeter in all 
low pressure boilers, and a sufficient height of chimney to 
enable the chimney to operate without a steam jet ; but it ia 
useful to know that a steam jet is a resource in the case of a de- 
fective boiler, or where the boiler has to be urged beyond its 
power. 

STEAM EOOM AND TRIMING. 

290. Q. — What is the capacity of steam room allowed in 
boilers per horse power ? 

A, — The capacity of steam room allowed by Boulton and 
Watt in their land wagon boilers is 8J cubic feet per horse 
power in the two horse power boiler, and 5J cubic feet in the 
20 horse power boiler ; and in the larger class of boilers, such 
as those suitable for 30 and 45 horse power engines, the capacity 
of the steam room does not fall below this amount, and, indeed, 
is nearer 6 than 5 J cubic feet per horse power. The content of 
water is 18| cubic feet per horse power in the two horse power 
boiler, and 15 cubic feet per horse power in the 20 horse power 
boiler. 

291. Q. — Is this the proportion Boulton and Watt allow in 
their marine boilers ? 

A. — Boulton and Watt in their early steam vessels were in 
the habit of allowing for the capacity of the steam space in 
marine boilers 16 times the content of the cylinder; but as there 
were two cylinders, this was equivalent to 8 times the content 



FLUCTUATIONS IN THE GENERATION OF STEAM. 141 

of both cylinders, wMch is the proportion commonly followed 
in land engines, and which agrees very nearly with the propor- 
tion of between 5 and 6 cubic feet of steam room per horse 
power already referred to. Taking for example an engine with 
23 inches diameter of cylinder and 4 feet stroke, which will be 
18*4 horse power — the area of the cylinder will be 415*476 
square inches, which, multiplied by 48, the number of inches in 
the stroke, will give 19942-848 for the capacity of the cylinder 
in cubic inches ; 8 times this is 159542*784 cubic inches, or 92*3 
cubic feet ; 92*3 divided by 18*4 is rather more than 5 cubic 
feet per horse power. 

292. Q. — ^Is the production of the steam in the boiler uni- 
form throughout the stroke of the engine ? 

A. — It varies with the slight variations in the pressure with- 
in the boiler throughout the stroke. Usually the larger part of 
the steam is produced during the first part of the stroke of the 
engine, for there is then the largest demand for steam, as the 
steam being commonly cut off somewhat before the end of the 
stroke, the pressure rises somewhat in the boiler during that 
period, and little steam is then produced. There is less neces- 
sity that the steam space should be large vv^hen the flow of steam 
from the boiler is very uniform, as it will be where there are 
two engines attached to the boiler at right angles with one an- 
other, or where the engines work at a great speed, as in the 
case of locomotive engines. A high steam chest too, by ren- 
dering boiling over into the steam pipes, or priming as it is 
called, more difficult, obviates the necessity for so large a steam 
space ; as does also a perforated steam pipe stretching through 
the length of the boiler, so as not to take the steam from one 
place. The use of steam of a high pressure, worked expansively, 
has the same operation ; so that in modern marine boilers, of 
the tubular construction, where the whole or most of these modi- 
fying circumstances exist, there is no necessity for so large a 
proportion of steam room as 5 or 6 cubic feet per nominal 
horse power, and about one, 1^, or 2 cubic feet of steam room 
per cubic foot of water evaporated, more nearly represents the 
general practice. 



142 NATURE OF PRIMING. 

293. Q. — Is this the proportion of steam room adopted in 
locomotive boilers ? 

A. — No ; in locomotive boilers the proportion of steam room 
per cubic foot of water evaporated is considerably less even 
than this. It does not usually exceed j of a cubic foot per cubic 
foot of water evaporated ; and with clean water, with a steam 
dome a few feet high set on the barrel of the boiler, or with a 
perforated pipe stretching from end to end of the barrel, and 
with the steam room divided about equally between the barrel 
and the fire box, very little priming is found to occur even with 
this smaU proportion of total steam room. About f the depth 
of the barrel is usually filled with water, and J with steam. 

294. ^.— What is priming ? 

A. — ^Priming is a violent agitation of the water within the 
boiler, in consequence of which a large quantity of water passes 
off with the steam in the shape of froth or spray. Such a result 
is injurious, both as regards the efficacy of the engine, and the 
safety of the engine and boiler ; for the large volume of hot 
water carried by the steam into the condenser impairs the va- 
cuum, and throws a great load upon the air pump, which 
diminishes the speed and available power of the engine ; and 
the existence of water within the cylinder, unless there be safe- 
ty valves upon the cylinder to permit its escape, will very 
probably cause some part of the machinery to break, by sud- 
denly arresting the motion of the piston when it meets the sur- 
face of the water, — the slide valve being closed to the condenser 
before the termination of the stroke, in all engines with lap 
upon the valves, so that the water within the cylinder is pre- 
vented from escaping in that direction. At the same time the 
boiler is emptied of its water too rapidly for the feed pump to 
be able to maintain the supply, and the flues are in danger of 
being burnt from a deficiency of water above them. 

295. Q. — What are the causes of priming ? 

A. — The causes of priming are an insufficient amount of 
steam room, an inadequate area of water level, an insufficient 
width between the flues or tubes for the ascent of the steam 
and the descent of water to supply the vacuity the steam occa' 



I 



REMEDIES FOR PRIMING. 143 

sions, and the use of dirty water in the boiler. New boilers 
prime more than old boilers, and steamers entering rivers from 
the sea are more addicted to priming than if sea or river water 
had alone been used in the boilers— probably from the boiling 
point of salt water being higher than that of fresh, whereby the 
salt water acts like so much molten metal in raising the fresh wa- 
ter into steam. Opening the safety valve suddenly may make a 
boiler prime, and if the safety valve be situated near the mouth 
of the steam pipe, the spray or foam thus created may be min- 
gled with the steam pasdng into the engine, and materially 
diminish its effective power ; but if the safety valve be situated 
at a distance from the mouth of the steam pipe, the quantity of 
foam or spray passing into the engine may be diminished by 
opening the safety valve ; and in locomotives, therefore, it is 
found beneficial to have a safety valve on the barrel of the 
boiler at a point remote from the steam chest, by partially 
opening which, any priming in that part of the boiler adjacent 
to the steam chest is checked, and a purer steam than before 
passes to the engine. 

296. Q. — What is the proper remedy for priming ? 

A. — When a boiler primes, the engineer generally closes the 
throttle valve partially, turns off the injection water, and opens 
the furnace doors, whereby the generation of steam is checked, 
and a less violent ebullition in the boiler suffices. Where the 
priming arises from an insufficient amount of steam room, it 
may be mitigated by putting a higher pressure upon the boiler 
and working more expansively, or by the interposition of a per- 
forated plate between the boiler and the steam chest, which 
breaks the ascending water and liberates the steam. In some 
cases, however, it may be necessary to set a second steam chest 
on the top of the existing one, and it will be preferable to es- 
tablish a communication with this new chamber by means of 
a number of small holes, bored through the iron plate of the 
boiler, rather than by a single large orifice. Where priming 
arises from the existence of dirty water in the boiler, the evil 
may be remedied by the use of collecting vessels, or by blowing 
off largely from the surface ; and where it arises from an in- 



144 MODE OF PROPORTIONING BOILERS. 

sufficient area of water level, or an insufficient width between 
the flues for the free ascent of the steam and the descent of the 
superincumbent water, the evil may be abated by the addition 
of circulating pipes in some part of the boiler, which will allow 
the water to descend freely to the place from whence the steam 
rises, the width of the water spaces being virtually increased 
by restricting their function to the transmission of a current of 
steam and water to the surface. It is desirable to arrange the 
heating surface in such a way that the feed water entering the 
boiler at its lowest point is heated gradually as it ascends, until 
toward the superior part of the flues it is raised gradually into 
steam ; but in all cases there will be currents in the boiler for 
which it is proper to provide. The steam pipe proceeding to 
the engine should obviously be attached to the highest point 
of the steam chest, in boilers of every construction. 

297. Q, — Having now stated the proportions proper to be 
adopted for evaporating any given quantity of water in steam 
boilers, will you proceed to show how you would proportion a 
boiler to do a given amount of work ? say a locomotive boiler 
which will propel a train of 100 tons weight at a speed of 50 
miles an hour. 

A. — According to experiments on the resistance of railway 
trains at various rates of speed, made by Mr. Gooch, of the Great 
Western Railway, it appears that a train weighing, with loco- 
motive, tender, and carriages, about 100 tons, experiences, at a 
speed of 50 miles an hour, a resistance of about 3,000 lbs., or 
about 30 lbs. per ton ; which resistance includes the resistance 
of the engine as well as that of the train. This, therefore, is 
the force which must be imparted at the circumference of the 
driving wheels, except that small part intercepted by the en- 
gine itself, and the force exerted by the pistons must be greater 
than that at the circumference of the driving wheel, in the pro- 
portion of their slower motion, or in the proportion of the cir- 
cumference of the driving wheel to the length of a double 
stroke of the engine. If the diameter of the driving wheel be 
5 J feet, its circumference will be 17'278 feet, and if the length 
of the stroke be 18 inches, the length of a double stroke will be 



t 



STRENGTH OF BOILERS. 145 



3 feet. The pressure on tlie pistons must therefore be greater 
than the traction at the circumference of the driving wheel, in 
the proportion of 17*278 to 3, or, in other words, the mean 
pressure on the pistons must be 17,278 lbs. ; and the area of 
cylinders, and pressure of steam, must be such as to produce 
conjointly this total pressure. It thus becomes easy to tell the 
volume and pressure of steam required, which steam in its turn 
represents its equivalent of water which is to be evaporated 
from the boiler, and the boiler must be so proportioned, by the 
rules already given, as to evaporate this water freely. In the 
case of a steam vessel, the mode of procedure is the same, and 
when the resistance and speed are known, it is easy to tell the 
equivalent value of steam. 

STRENGTH OF BOILERS. 

298. ^.— What strain should the iron of boilers be subjected 
to in working ? 

A. — The iron of boilers, like the iron of machines or struc- 
tures, is capable of withstanding a tensile strain of from 50,000 
to 60,000 lbs. upon every square inch of section ; but it will 
only bear a third of this strain without permanent derangement 
of structure, and it does not appear expedient in any boiler to 
let the strain exceed 4,000 lbs. upon the square inch of sectional 
area of metal, especially if it is liable to be weakened by cor- 
rosion. 

299. Q, — Have any experiments been made to determine the 
strength of boilers ? 

A. — The question of the strength of boilers was investigated 
very elaborately a few years ago by a committee of the Franklin 
Institute, in America, and it was found that the tenacity of boil- 
er plate increased with the temperature up to 550°, at which 
point the tenacity began to diminish. At 32°, the cohesive 
force of a square inch of section was 56,000 lbs. ; at 570°, it was 
66,500 lbs. ; at 720°, 55,000 lbs. ; at 1,050^, 32,000 lbs. ; at 
1,240^, 22,000 lbs. ; and at 1,317°, 9,000 lbs. Copper follows a 
different law, and appears to be diminished in strength by 



146 FRANKLIN INSTITUTE ^MR. FAIRBAIRN. 

every addition to the temperature. At 32° the cohesion of cop- 
per was found to be 32,800 lbs. per square inch of section, which 
exceeds the cohesive force at any higher temperature, and the 
square of the diminution of strength seems to keep pace with 
the cube of the increased temperature. Strips of iron cut in the 
direction of the fibre were found to be about 6 per cent, stronger 
than when cut across the grain. Repeated piling and welding 
was found to increase the tenacity of the iron, but the result of 
welding together different kinds of iron was not found to be 
favorable. The accidental overheating of a boiler was found to 
reduce the ultimate or maximum strength of the plates from 
65,000 to 45,000 lbs. per square inch of section, and riveting 
the plates was found to occasion a diminution in their strength 
to the extent of one third. These results, however, are not pre- 
cisely the same as those obtained by Mr. Fairbairn. 

300. Q. — What were the results obtained by him ? 

A. — He found that boiler plate bore a tensile strain of 23 
tons per square inch before rupture, which was reduced to 16 
tons per square inch when joined together by a double row of 
rivets, and 13 tons, or about 30,000, w^hen joined together by a 
single row of rivets. A circular boiler, therefore, with the ends 
of its plates double riveted, will bear at the utmost about 36,00< 
lbs. per square inch of section, or about 12,000 lbs. per squa: 
inch of section without permanent derangement of structure, 

301. Q. — Wliat pressure do cylindrical boilers sustain i 
practice ? 

A. — In some locomotive boilers, which are worked mth 
pressure of 80 lbs. upon the square inch, the thickness of the 
plates is only y^^ths of an inch, while the barrel of the boiler is 
39 inches in diameter. It will require a length of 3*2 mches of 
the boiler when the j)lates are y^ths thick to make up a section-^ 
al area of one square inch, and the separating force will be 3! 
times 3'2 multij^lied by 80, which makes the separating force 9,984 
lbs., sustained by two square inches of sectional area — one on 
each side ; or the strain is 4,992 lbs. per square inch of sectional 
area, which is quite as great strain as is advisable. The acces- 
sion of strength derived from the boiler ends is not here taken 



4 1 



RULES FOR THICKNESS OF BOILERS. 147 

into account, but neither is the weakening effect counted that is 
caused by the rivet holes. Some locomotives of 4 feet diameter 
of barrel and of Jths iron have been worked to as high a press- 
ure as 200 lbs. on the inch ; but such feats of daring are neither 
to be imitated nor commended. 

302. Q. — Can you give a rule for the proper thickness of 
cylindrical boilers ? 

A. — The thickness proper for cylindrical boilers of wrought 
iron, exposed to an internal pressure, may be found by the fol- 
lowing rule : — multiply 2*54 times the internal diameter of the 
cylinder in inches by the greatest pressure within the cylinder 
per circular inch, and divide by 17,800 ; the result is the thick- 
ness in inches. If we apply this rule to the example of the 
locomotive boiler just given, we have 39 x 2*54 x 62-832 (the 
pressure per circular inch corresponding to 80 lbs. per square 
inch) =6224-1379, and this, divided by 17,800, gives 0-349 as 
the thickness in inches, instead of 0'3125, or y^ths, the actual 
thickness. If we take the pressure per square inch instead of 
per circular inch, we obtain the following rule, which is some- 
what simpler : — multiply the internal diameter of the. cylinder 
in inches by the pressure in pounds per square inch, and divide 
the product by 8,900 ; the result is the thickness in inches. 
Both these rules give the strain about one fourth of the elastic 
force, or 4,450 lbs. per square inch of sectional area of the iron ; 
but 3,000 lbs. is enough when the flame impinges directly on 
the iron, as in some of the ordinary cylindrical boilers, and the 
rule may be adapted for that strain by taking 6,000 as a divisor 
instead of 8,900. 

303. Q. — In marine and wagon boilers, which are not of a 
cylindrical form, how do you procure the requisite strength ? 

^. — Where the sides of the boiler are flat, instead of being 
cylindrical, a sufficient number of stays must be introduced to 
withstand the pressure ; and it is expedient not to let the strain 
upon these stays be more than 3,000 lbs. per square inch of sec- 
tion, as the strength of internal stays in boilers is generally soon 
diminished by corrosion. Indeed, a strain at all approaching 
that upon locomotive boilers would be very unsafe in the case 



148 THE STAYING OF BOILERS. 

of marine boilers, on account of the corrosion, both internal and 
external, to which marine boilers are subject. The stays should 
be small and numerous rather than large and few in number, 
as, when large stays are employed, it is difficult to keep them 
tight at the ends, and oxidation of the shell follows from leak- 
age at the ends of the stays. All boilers should be proved, when 
new, to twice or three times the pressure they are intended to 
bear, and they should be proved occasionally by the hand pump 
when in use, to detect any weakness which corrosion may have 
occasioned. 

304. §.— Will you describe the disposition of the stays in 
a marine boiler ? 

A. — If the pressure of steam be 20 lbs. on the square inch, 
which is a very common pressure in tubular boilers, there will 
be a pressure of 2,880 lbs. on every square foot of flat surface ; so 
that if the strain upon the stays is not to exceed 3,000 lbs. on 
the square inch of section, there must be nearly a square inch of 
sectional area of stay for every square foot of flat surface on the 
top and bottom, sides, and ends of the boiler. This very much 
exceeds the proportion usually adopted ; and in scarcely any in- 
stance are boilers stayed sufficiently to be safe w^hen the shell is 
composed of flat surfaces. The furnaces should be stayed to- 
gether with bolts of the best scrap iron, 1^ inch in diameter, 
tapped through both plates of the w^ater space with thin nuts 
in each furnace ; and it is expedient to make the row of stays, 
running horizontally near the level of the bars, sufficiently low 
to come beneath the top of the bars, so as to be shielded from 
the action of the fire, with which view they should follow the 
inclination of the bars. The row of stays between the level of 
the bars and the top of the furnace should be as near the top 
of the furnace as will consist with the functions they have to^ 
perform, so as to be removed as far as possible from the actio; 
of the heat ; and to support the furnace top, cross bars ma; 
either be adopted, to which the top is secured with bolts, as irf 
the case of locomotives, or stays tapped into the furnace top, 
with a thin nut beneath, may be carried to the top of the 
boiler ; but very little dependence can be put in such stays as 



I 



i 



THE STAYING OF BOILERS. 149 

stays for keeping down the top of the boiler ; and the top of 
the boiler must, therefore, be stayed nearly as much as if the 
stays connecting it with the furnace crowns did not exist. The 
large rivets passing through thimbles, sometimes used as stays 
for water spaces or boiler shells, are objectionable; as, from the 
great amount of hammering such rivets have to receive to form 
the heads, the iron becomes crystalline, so that the heads are 
liable to come oflF, and, indeed, sometimes fly off in the act of 
being formed. If such a fracture occurs between the boilers 
after they are seated in their place, or in any position not ac- 
cessible from the outside, it will in general be necessary to emp- 
ty the faulty boiler, and repair the defect from the inside. 

805. Q. — What should be the pitch or numerical distribution 
of the stays ? 

A. — The stays, where the sides of the boiler are flat, and the 
pressure of the steam is from 20 to 30 lbs., should be pitched 
about a foot or 18 inches asunder; and in the wake of the 
tubes, where stays cannot be carried across to connect the 
boiler sides, angle iron ribs, like the ribs of a ship, should be 
riveted to the interior of the boiler, and stays of greater 
strength than the rest should pass across, above, and below the 
tubes, to which the angle irons would communicate the strain. 
The whole of the long stays within a boiler should be firmly 
riveted to the shell, as if built with and forming a part of it ; 
as, by the common method of fixing them in by means of cut- 
ters, the decay or accidental detachment of a pin or cutter may 
endanger the safety of the boiler. Wherever a large perforation 
in the shell of any circular boiler occurs, a sufficient number of 
stays should be put across it to maintain the original strength ; 
and where stays are intercepted by the root of the funnel, short 
stays in continuation of them should be placed inside. 

BOILER EXPLOSIONS. 

306. Q. — What is the chief cause of boiler explosions ? 
A, — The chief cause of boiler explosions is, undoubtedly, 
too great a pressure of steam, or an insufficient strength of 



150 CHIEF CAUSE OF BOILER EXPLOSIONS. 

boiler ; but many explosions have also arisen from the flues having 
been suffered to become red hot. If the safety valve of a boiler 
be accidentally jammed, or if the plates or stays be much worn 
by corrosion, while a high pressure of steam is nevertheless 
maintained, the boiler necessarily bursts ; and if, from an in- 
sufficiency of water in the boiler, or from any other cause, the 
flues become highly heated, they may be forced down by the 
pressure of the steam, and a partial explosion may be the result. 
The worst explosion is where the shell of the boiler bursts } but 
the collapse of a furnace or flue is also very disastrous generally 
to the persons in the engine room ; and sometimes the shell 
bursts and the flues collapse at the same time ; for if the flues 
get red hot, and water be thrown upon them either by the feed 
pump or otherwise, the generation of steam may be too rapid 
for the safety valve to permit its escape with sufficient facility, 
and the shell of the boiler may, in consequence, be rent asunder. 
Sometimes the iron of the flues becomes highly heated in con- 
sequence of the improper configuration of the parts, which, by 
retaining the steam in contact with the metal, prevents the ac- 
cess of the water : the bottoms of large flues, upon which the 
flame beats down, are very liable to injury from this cause ; and 
the iron of flues thus acted upon may be so softened that the 
flues will collapse upward with the pressure of the steam. The 
flues of boilers may also become red hot in some parts from the 
attachment of scale, which, from its imperfect conducting power, 
will cause the iron to be unduly heated ; and if the scale be acci- 
dentally detached, a partial explosion may occur in consequence. 

307. Q. — Does the contact of water with heated metal occa- 
sion an instantaneous generation of steam ? 

A. — It is found that a sudden disengagement of steam doe3 
not immediately follow the contact of water with the hot metal, 
for water thrown upon red hot iron is not immediately con- 
verted into steam, but assumes the spheroidal form and rolls 
about in globules over the surface. These globules, however 
high the temperature of the metal may be on which they are 
placed, never rise above the temperature of 205°, and give off 
but very little steam ; but if the temperature of the metal be 



)i 



I 



STICKING OF SAFETY VALVES. 151 



lowered, tho water ceases to retain tlie spheroidal form, and 
comes into intimate contact with the metal, whereby a rapid 
disengagement of steam takes place. If water be poured into a 
very hot copper flask, the flask may be corked up, as there will 
be scarce any steam produced so long as the high temperature 
is maintained ; but so soon as the temperature is suffered to fall 
below 350"^ or 400°, the spheroidal condition being no longer 
maintainable, steam is generated with rapidity, and the cork 
will be projected from the mouth of the flask with great force. 

308. Q. — What precautions can be taken to prevent boiler 
explosions ? 

-4.— One useful precaution against the explosion of boilers 
from too great an internal pressure, consists in the application 
of a steam gauge to each boiler, which will make the existence 
of any undue pressure in any of the boilers immediately visible ; 
and every boiler should have a safety valve of its own, the pass- 
age leading to which should have no connection with the pass- 
age leading to any of the stop valves used to cut off the con- 
nection between the boilers ; so that the action of the safety 
valve may be made independent of the action of the stop valve. 
In some cases stop valves have jammed, or have been carried 
from their seats into the mouth of the pipe communicating 
between them, and the action of the safety valves should be 
rendered independent of all such accidents. Safety valves, 
themselves, sometimes stick fast from corrosion, from the spin- 
dles becoming bent, from a distortion of the boiler top with a 
high pressure, in consequence of which the spindles become 
jammed in the guides, and from various other causes which it 
would be tedious to enumerate ; but the inaction of the safety 
valves is at once indicated by the steam gauge, and when dis- 
covered, the blow through valves of the engine and blow off 
cocks of the boiler should at once be opened, and the fires raked 
out. A cone in the ball of the waste steam pipe to send back 
the water carried upward by the steam, should never be insert- 
ed ; as in some cases this cone has become loose, and closed up 
the mouth of the waste steam pipe, whereby the safety valves 
being rendered inoperative, the boiler was in danger of bursting. 



152 DANGERS OF EXCESSIVE PEIMING. 

309. Q. — May not danger arise from excessive priming ? ^ 
A. — If the water be carried out of the boiler so rapidly by! 

priming that the level of the water cannot be maintained, and 
the flues or furnaces are in danger of becoming red hot, tha 
best plan is to open every furnace door and throw in a few 
buckets full of water upon the fire, taking care to stand suf- 
ficiently to the one side to avoid being scalded by the rush of' 
steam from the furnace. There is no time to begin drawing the 
fires in such an emergency, and by this treatment the fires, 
though not altogether extinguished, will be rendered incapable 
of doing harm. If the flues be already red hot, on no account 
must cold water be suffered to enter the boiler, but the heat 
should be maintained in the furnaces, and the blow off cocks be 
opened, or the mud hole doors loosened, so as to let all the 
water escape ; but at the same time the pressure must be kept 
quite low in the boiler, so that there will be no danger of the 
hot flues collapsing with the pressure of the steam. 

310. Q, — Are plugs of fusible metal useful in preventing ex- 
plosions ? 

A. — Plugs of fusible metal were at one time in much repute 
as a precaution against explosion, the metal being so com- 
pounded that it melted with the heat of high pressure steam ; 
but the device, though ingenious, has not been found of any 
utility in practice. The basis of fusible metal is mercury, and 
it is found that the compound is not homogeneous, and that 
the mercury is forced by the pressure of the steam out of the 
interstices of the metal combined with it, leaving a porouSj 
metal which is not easily fusible, and which is, therefore, unabL 
to perform its intended function. In locomotives, however, andj 
also in some other boilers, a lead rivet is inserted with advan-j 
tage in the crown of the flre box, which is melted out if the 
water becomes too low, and thus gives notice of the danger. 

311. Q. — May not explosion occur in marine boilers from 
the accumulation of salt on the flues ? 

A. — Yes, in marine boilers this is a constant source of danger^ 
which is only to be met by attention on the part of the engi- 
neer. If the water in the boiler be suffered to become too salt,] 



I 



DANGERS OF ACCUMULATION OF SALT. 163 

an incrustation of salt will take place on tlie furnaces, which 
may cause them to become red hot, and they may then be col- 
lapsed even by their own weight aided by a moderate pressure 
of steam. The expedients which should be adopted for pre- 
venting such an accumulation of salt from taking place within 
the boiler as will be injurious to it, properly fall under the head 
of the management of steam boilers, and will be explained in a 
subsequent chapter. 



CHAPTER VI. 



PROPORTIONS OF ENGINES. 



STEAM PASSAGES. 



312. Q. — ^What size of orifice is commonly allowed for the 
escape of the steam through the safety valve in low pressure 
engines ? 

A. — About 0*8 of a circular inch per horse power, or a cir- 
cular inch per IJ horse power. The following rule, however, 
will give the dimensions suitable for all kinds of engines, 
whether high or low pressure: — multiply the square of the 
diameter of the cylinder in inches by the speed of the piston in 
feet per minute, and divide the product by 375 times the pressure 
on the boiler per square inch ; the quotient is the proper area 
of the safety valve in square inches. This rule of course supposes 
that the evaporating surface has been properly proportioned to 
the engine power. 

313. Q, — Is this rule applicable to locomotives ? 

A. — It is applicable to high pressure engines of every kind. 
The dimensions of safety valves, however, in practice are very 
variable, being in some cases greater, and in some cases less, 
than what the rule gives, the consideration being apparently as 
often what proportions will best prevent the valve from sticking 



1 



PROPER DIMENSIONS OF SAFETY VALVES. 155 



in its seat, as wliat proportions will enable the steam to escape 
freely. In Bury's locomotives, the safety valve was generally 
2h inches diameter for all sizes of boiler, and the valve was kept 
down by a lever formed in the proportion of 5 to 1, fitted at 
one end with a Salter's balance. As the area of the valve was 
5 square inches, the number of pounds shown on the spring 
balance denoted the number of pounds pressure on each square 
inch of the boiler. 

314. ^.— Is there only one safety valve in a locomotive 
boiler ? 

A.— There are always two. 

315. Q. — And are they always pressed uown by a spring 
balance, and never by weights ? 

A, — They are never pressed down by weights; in fact, 
weights would not answer on a locomotive at all, as they would 
jump up and down with the jerks or jolts of the train, and 
cause much of the steam to escape. In land and marine boilers, 
however, the safety valve is always kept down by weights ^ but 
in steam vessels a good deal of steam is lost in stormy weather 
by the openiDg of the valve, owing to the inertia of the weights 
when the ship sinks suddenly in the deep recess between the 
waves. 

316. Q. — What other sizes of safety valves are used in loco- 
motives ? 

A. — Some are as large as 4 inches diameter, giving 12 square 
inches of area; and others are as small as 1-j^ inch diameter, 
giving 1 square inch of area. 

317. ^.— And are these valves all pressed down by a Salter's 
spring balance ? 

A, — In the great majority of cases they are so, and the lever 
by which they are pressed down is generally ^rraduated in the 
proportion of the area of the valve to unity ; that is, in the case 
of a valve of 13 inches area, the long end of the lever to which 
the spring balance is attached is 13 times the length of the 
short end, so that the weight or pressure on the balance shows 
the pressure per square inch on the boiler. In some cases, how- 
ever, a spiral spring, and in other cases a pile of elliptical 



156 PROPER DIMENSIONS OF STEAM PASSAGES. 

springs, is placed directly upon tlie top of the valve, and it 
appears desirable that one of the valves at least should be 
loaded in this manner. It is difficult when the lever is divided 
in such a proportion as 12 to 1, to get sufficient lift of the valve 
without a large increase of pressure on the spring ; and it ap- 
pears expedient, therefore, to employ a shorter lever, which 
involves either a reduction in the area of the valve, or an 
increased strength in the spring. 

318. Q. — What are the proper dimensions of the steam pas- 



A, — In slow working engines the common size of the cylin- 
der passages is one twenty-fifth of the area of the cylinder, or 
one fifth of the diameter of the cylinder, which is the same 
thing. This proportion corresponds very nearly with one 
square inch per horse power when the length of the cylinder 
is about equal to its diameter ; and one square inch of area per 
horse power for the cylinder ports and eduction passages 
answers very well in the case of engines working at the ordi- 
nary speed of 220 feet per minute. The area of the steam pipe 
is usually made less than the area of the eduction pipe, espe- 
cially when the engine is worked expansively, and with a con- 
siderable pressure of steam. In the case of ordinary condensing 
engines, however, working with the usual pressure of from 4 to 
8 lbs. above the atmosphere, the area of the steam pipe is not 
less than a circular inch per horse power. In such engines the 
diameter of the steam pipe may be found by the following rule : 
divide the number of nominal horse power by 0*8 and extract 
the square root of the quotient, which will be the internal 
diameter of the steam pipe. 

319. Q. — Will you explain by what process of computation 
these proportions are arrived at ? 

A, — The size of the steam pipe is so regulated that there 
will be no material disparity of pressure between the cylinder 
and boiler ; and in fixing the size of the eduction passage the 
same object is kept in view. When the diameter of the cylin- 
der and the velocity with which the piston travels are known, 
it is easy to tell what the velocity of the steam in the steam 



HIGH SPEED ENGINES EEQUIRE LAKGER PASSAGES. 157 

pipe will be ; for if the area of the cylinder be 25 times greater 
than that of the steam pipe, the steam in the steam pipe must 
travel 25 times faster than the piston, and the difference of press- 
ure requisite to produce this velocity of the steam can easily be 
ascertained, by finding vrhat height a column of steam must be 
to give that velocity, and what the weight or pressure is of such 
a column. In practice, however, this proportion is always 
exceeded from the condensation of steam in the pipe. 

320. Q, — If the relation you have mentioned subsist between 
the area of the steam passages and the velocity of the piston, 
then the passages mast be larger when the piston travels very 
rapidly ? 

A. — And they are so made. The area of the ports of loco- 
motive engines is usually so proportioned as to be from J^th to 
^th the area of the cylinder — in some cases even as much as ^th ; 
and in all high speed engines the ports should be very large, 
and the valve should have a good deal of travel so as to open 
the port very quickly. The area of port which it appears 
advisable to give to modern engines of every description, is 
expressed by the following rule : — multiply the area of the cylin- 
der in square inches by the speed of the piston in feet per min- 
ute, and divide the product by 4,000 ; the quotient is the area 
of each cylinder port in square inches. This rule gives rather 
more than a square inch of port per nominal horse power to 
condensing engines working at the ordinary speed ; but the 
excess is but small, and is upon the right side. For engines 
travelling very fast it gives a good deal more area than the ' 
common proportion, which is too small in nearly every case. 
In locomotive engines the eduction pipe passes into the chimney 
and the force of the issuing steam has the effect of maintaining 
a rapid draught through the furnace as before explained. The 
orifice of the waste steam pipe, or the blast pipe as it is termed, 
is much contracted in some engines with the view of producing 
a fiercer draught, and an area of ^^^jd of the cylinder is a com- 
mon proportion ; but this is as much contraction as should be 
allowed, and is greater than is advisable. 

321. Q. — In engines moving at a high rate of speed, you 



158 ADVANTAGES OF LAP AND LEAD. 

have stated that it is important to give the valve lead, or in 
other words to allow the steam to escape before the end of the 
stroke ? 

A. — Yes, this is very important, else the piston will have to 
force out the steam from the cylinder, and will be much resist- 
ed. Near the end of the stroke the piston begins to travel 
slowly, and if the steam be then permitted to escape, very little 
of the eflfective stroke is lost, and time is afforded to the steam, 
before the motion of the piston is again accelerated, to make its 
escape by the port. In some locomotives, from inattention to 
this adjustment, and from a contracted area of tube section, 
which involved a strong blast, about half the power of the 
engine has been lost ; but in more recent engines, by using 
enlarged ports and by giving sufficient lead, this loss has been 
greatly diminished. 

322. Q.— What do you call sufficient lead ? 

A, — In fast going engines I would call it sufficient lead, 
when the eduction port was nearly open at the end of the 
stroke. 

323. Q, — Can you give any example of the benefit of increas- 
ing the lead ? 

A. — The early locomotives were made with very little lead, 
and the proportions were in fact very much the same as those 
previously existing in land engines. About 1832, the benefits 
of lap upon the valve, which had been employed by Boulton 
and Watt more than twenty years before, were beginning to be 
pretty generally apprehended ; and, in the following year, this 
expedient of economy was applied to the steamer Manchester, 
in the Clyde, and to some other vessels, with very marked suc- 
cess. Shortly after this time, lap began to be applied to the 
valves of locomotives, and it was found that not only was there 
a benefit from the operation of expansion, but that there was a 
still greater benefit from the superior facility of escape given to 
the steam, inasmuch as the application of lap involved the 
necessity of turning the eccentric round upon the shaft, which 
caused the eduction tio take place before the end of the stroke. 
In 1840, one of the engines of the Liverpool and Manchester 



PEOPER PROPORTIONS OF AIR PUMP AND CONDENSER. 159 

Railway was altered so as to have 1 inch lap on the valve, and 
1 inch opening on the eduction side at the end of the stroke, 
the valve having a total travel of 4} inches. The consumption 
of fuel per mile fell from 36*3 lbs. to 28*6 lbs, or about 25 per 
cent., and a softer blast sufficed. By using larger exhaust pass- 
ages, larger tubes, and closer fire bars, the consumption was 
subsequently brought down to 15 lbs. per mile. 



AIPw PUMP, CONDENSER, AND HOT AI^D COLD WATER PUMPS. 

324. Q. — ^Will you state the proper dimensions of the air 
pump and condenser in land and marine engines ? 

A. — Mr. Watt made the air pump of his engine half the 
diameter of the cylinder and half the stroke, or one eighth of 
the capacity, and the condenser was usually made about the 
same size as the air pump ; but as the pressure of the steam has 
been increased in all modem engines, it is better to make the air 
pump a little larger than this proportion. 0*6 of the diameter 
of the cylinder and half the stroke answers very well, and the 
condenser may be made as large as it can be got with con- 
venience, though the same size as the air pump will suffice. 

325. Q. — Are air pumps now sometimes made double acting ? 

A. — Most of the recent direct acting marine engines for dri- 
ving the screw are fitted with a double acting air pump, and 
when the air pump is double acting, it need only be about half 
the size that is necessary when it is single acting. It is single 
acting in nearly every case, except the case of direct acting 
screw engines of recent construction. 

326. Q. — What is the difierence between a single and a 
double acting air pump ? 

A. — The single acting air pump expels the air and water 
from the condenser only in the upward stroke of the pump, 
whereas a double acting air pump expels the air and water both 
in the upward and downward stroke. It has, therefore, to be 
provided with inlet and outlet valves at both ends, whereas the 
single acting pump has only to be provided with an inlet or 
foot valve, as it is termed, at the bottom, and with an outlet or 



160 SINGLE ACTING AND DOUBLE ACTING AIR PUMPS. 

delivery valve, as it is termed, at the top. The single acting 
air pump requires to be provided with a valve or valves in the 
piston or bucket of the pump, to enable the air and water lying 
below the bucket when it begins to descend, and which have 
entered from the condenser during the upward stroke, to pass 
through the bucket into the space above it during the down- 
ward stroke, from whence they are expelled into the atmo- 
sphere on the upward stroke succeeding. But in the double 
acting air pump no valve is required in the piston or bucket of 
the pump, and all that is necessary is an inlet and outlet valve 
at each end. 

327. Q. — What are the dimensions of the foot and discharge 
valves of the air pump ? 

A. — The area through the foot and discharge valves is usu- 
ally made equal to one fourth of the area of the air pump, and 
the diameter of the waste water pipe is made one fourth of the 
diameter of the cylinder, which gives an area somewhat less 
than that of the foot and discharge valve passages. But this 
proj^ortion only applies in slow engines. In fast engines, with 
the air pump bucket moving as fast as the piston, the area 
through the foot and discharge valves should be equal to the 
area of the pump itself, and the waste water pipe should be of 
about the same dimensions. 

328. Q. — ^You have stated that double acting air pumps need 
only be of half the size of single acting ones. Does that relation 
hold at all speeds ? 

A. — It holds at all speeds if the velocity of the pump buck- 
ets are in each case the same ; but it does not hold if the engine 
with the single acting pump works slowly, and the engine with 
the double acting pump moves rapidly, as in the case of direct 
acting screw engines. All pumps moving at a high rate of 
speed lose part of their efficiency, and such pumps should there- 
fore be of extra size. 

329. Q. — How do you estimate the quantity of water requi- 
site for condensation ? 

A. — Mr. Watt found that the most beneficial temperature of 
the hot well of his engines was 100 degrees. If, therefore, the 



TOO MUCH INJECTION INJURIOUS. 161 

temperature of the steam be 212°, and tlie latent heat 1,000°, 
then 1,212° may be taken to represent the heat contained in the 
steam, or 1,112° if we deduct the temperature of the hot well. 
If the temperature of the injection water be 50°, then 50 degrees 
of cold are available for the abstraction of heat ; and as the 
total quantity of heat to be abstracted is that requisite to raise 
the quantity of water in the steam 1,112 degrees, or 1,112 times 
that quantity one degree, it would raise one fiftieth of this, or 
22*24 times the quantity of water in the steam, 50 degrees. A 
cubic inch of water therefore raised into steam will require 
22*24 cubic inches of water at 50 degrees for its condensation, 
and will form therewith 23*24 cubic inches of hot water at 100 
degrees. Mr. Watt's practice was to allow about a wine pint 
(28*9 cubic inches) of injection water, for every cubic inch of 
water evaporated from the boiler. 

330. Q. — Is not a good vacuum in an engine conducive to 
increased power ? 

^.— It is. 

831. Q. — And is not the vacuum good in the proportion in 
which the temperature is low, supposing there to be no air 
leaks ? 

^.— Yes. 

332. §.— Then how could Mr. Watt find a temperature of 
100° in the water drawn from the condenser, to be more bene- 
ficial than a temperature of 70° or 80°, supposing there to be 
an abundant supply of cold water ? 

333. A. — Because the superior vacuum due to a temperature 
of 70° or 80° involves the admission of so much cold water into 
the condenser, which has afterward to be pumped out in oppo- 
sition to the pressure of the atmosphere, that the gain in the 
vacuum does not equal the loss of power occasioned by the 
additional load upon the pump, and there is therefore a clear 
loss by the reduction of the temperature below 100°, if such 
reduction be caused by the admission of an additional quantity 
of water. If the reduction of temperature, however, be caused 
by the use of colder water, there is a gain produced by it, 
though the gain will within certain limits be greater if advan- 



162 PROPER AREA OP INJECTION ORIFICE. 

tage be taken of the lowness of the temperature to diminish the 
quantity of injection. 

334. Q. — How do you determine the proper area of the in- 
jection orifice ? 

A. — The area of the injection orifice proper for any engine 
can easily be told when the quantity of water requisite to con- 
dense the steam is known, and the pressure is specified under 
which the water enters the condenser. The vacuum in the con- 
denser may be taken at 26 inches of mercury, which is equiva- 
lent to a column of water 29*4 ft. high, and the square root of 
29-4 multiplied by 8'021 is 43*15, which is the velocity in feet 
per second that a heavy body would acquire in falling 29*4 ft., 
or with which the water would enter the condenser. Now, if a 
cubic foot of water evaporated per hour be equivalent to an 
actual horse power, and 28'9 cubic inches of water be requisite 
for the condensation of a cubic inch of water in the form of 
steam, 28*9 cubic feet of condensing water per horse power per 
hour, or 13*905 cubic inches per second, will be necessary for 
the engine, and the size of the injection orifice must be such 
that this quantity of water flowing with the velocity of 43*15 
ft. per second, or 517*8 inches per second, will gain admission 
to the condenser. Dividing, therefore, 13*905, the number of 
cubic inches to be injected, by 517*8, the velocity of influx in 
inches per second, we get 0*02685 for the area of the orifice in 
square inches; but inasmuch as it has been found by experi- 
ment that the actual discharge of water through a hole in a 
thin plate is only six tenths of the theoretical discharge on 
account of the contracted vein, the area of the orifice must be 
increased in the proportion of such diminution of efiect, or be 
made 0*04475, or -^di of a square inch per horse power. This, 
it will be remarked, is the theoretical area required per actual 
horse power ; but as the friction and contractions in the pipe 
further reduce the discharge, the area is made y^^th of a square 
inch per actual horse power, or rather per cubic foot of water 
evaporated from the boiler. 

335. Q. — Cannot the condensation of the steam be accom- 
plished by any other means than by the admission of cold water 
into the condenser ? 



PROPER SIZE OF FEED PUMP. 163 

A. — It maybe accomplislied by the method of external cold, 
as it is called, which consists in the application of a large num- 
ber of thin metallic surfaces to the condenser, on the one side 
of which the steam circulates, while on the other side there is a 
constant current of cold water, and the steam is condensed b}'^ 
coming into contact with the cold surfaces, without mingling 
with the water used for the purpose of refrigeration. The first 
kind of condenser employed by Mr. Watt was constructed after 
this fashion, but he found it in practice to be inconvenient 
from its size, and to become furred up or incrusted when the 
water was bad, whereby the conducting power of the metal was 
impaired. He therefore reverted to the use of the jet of cold 
water, as being upon the whole preferable. The jet entered the 
condenser instead of the cylinder as was the previous practice, 
and this method is now the one in common use. Some few 
years ago, a good number of steam vessels were fitted with 
Hall's condensers, which operated on the principle of external 
cold, and which consisted of a faggot of small copper tubes 
surrounded by water ; but the use of those condensers has not 
been persisted in, and most of the vessels fitted with them have 
returned to the ordinary plan. 

336. Q, — You stated that the capacity of the feed pump 
was oloth of the capacity of the cylinder in the case of con- 
densing engines, — the engine being double acting and the 23ump 
single acting, — and that in high pressure engines the capacity 
of the pump should be greater in proportion to the pressure of 
the steam. Can you give any rule that will express the proper 
capacity for the feed pump at all pressures ? 

A. — That will not be difficult. In low pressure engines the 
pressure in the boiler may be taken at 5 lbs. above the atmo- ; 
spheric pressure, or 20 lbs. altogether ; and as high pressure 
steam is merely low pressure steam compressed into a smaller 
compass, the size of the feed pump in relation to the size of the 
cylinder must obviously varj^ in the direct proportion of the 
pressure ; and if it be aJo^h of the capacity of the cylinder 
when the total pressure of the steam is 20 lbs., it must be -ploth 
of the capacity of the cylinder when the pressure is 40 lbs. per 



164 DEFECTIVE ACTION OF ORDINARY PUMPS. 

square inch, or 25 lbs. per square incli above the atmospheric 
pressure. This law of variation is expressed by the following 
rule : — multiply the capacity of the cylinder in cubic inches by 
the total pressure of the steam in lbs. per square inch, or the 
pressure per square inch on the safety valve plus 15, and divide 
the product by 4,800 ; the quotient is the capacity of the feed 
pump in cubic inches, when the feed pump is single acting and 
the engine double acting. If the feed pump be double acting, 
or the engine single acting, the capacity of the pump must just 
be one half of what is given by this rule. 

337. Q. — But should not some addition be made to the size 
of pump thus obtained if the pump works at a high rate of 
speed ? 

A. — No ; this rule makes allowance for defective action. All 
pumps lift much less water than is due to the size of their 
barrels and the number of their strokes. Moderately good 
pumps lose 50 per cent, of their theoretical effect, and bad 
pumps 80 per cent. 

338. Q. — To what is this loss of effect to be chiefly ascribed ? 
A. — ^IVIainly to the inertia of the water, which, if the pump 

piston be drawn up very rapidly, cannot follow it with sufficient 
rapidity ; so that there may be a vacant space between the pis- 
ton and the water ; and at the return stroke the momentum of 
the water in the pipe expends itself in giving a reverse motion 
to the column of water approaching the pump. Messrs. Kirch- 
weger and Prusman, of Hanover, have investigated this subject 
by applying a revolving cock at the end of a pipe leading from 
an elevated cistern containing water, and the water escaped at 
every revolution of the cock in the same manner as if a pump 
were drawing it. With a column of water of 17 feet, they found 
that at 80 revolutions of the cock per minute, the water deliv- 
ered per minute by the cock was 9*45 gallons; but with 140 
revolutions of the cock per minute, the water delivered per 
minute by the cock was only 5*42 gallons. They^ubsequently 
applied an air vessel to the pipe beside the cock, when the dis- 
charge rose to 12*9 gallons per minute with 80 revolutions, and 
18*28 gallons with 140 revolutions. Air vessels should there- 



d 



PEOPORTIONS PROPER FOR THE FLY WHEEL. 165 

fore be applied to the suction side of fast moving pumps, and 
this is now done with good results. 

339. Q. — What are the usual dimensions of the cold water 
pump of land engines ? 

A. — If to condense a cubic inch of water raised into steam 
28*9 cubic inches of condensing water are required, then the 
cold water pump ought to be 28*9 times larger than the feed 
pump, supposing that its losses were equally great. The feed 
pump, however, is made sufficiently large to compensate for 
leaks in the boiler and loss of steam through the safety valve, 
so that it will be sufficient if the cold water pump be 24 times 
larger than the feed pump. This ratio is preserved by the fol- 
lowing rule : — multiply the capacity of the cylinder in cubic 
inches by the total pressure of the steam per square inch, or the 
pressure on the safety valve plus 15, and divide the product by 
200. The quotient is the proper capacity of the cold water 
pump in cubic inches when the engine is double acting, and the 
pump single acting. 

FLY WHEEL. '^'*^ 

340. Q. — By what considerations do you determine the 
dimensions of the fly wheel of an engine ? 

A. — By a reference to the power generated, each half stroke 
of the engine, and the number of half strokes that are necessary 
to give to the fly wheel its standard velocity, supposing the 
whole power devoted to that object. In practice the power 
resident in the fly varies from 2^ to 6 times that generated each 
half stroke ; and if the weight of the wheel be equal to the 
pressure on the piston, its velocity must be such as it would 
acquire by falling through a height equal to from 2^ to 6 times 
the stroke, according to the purpose for which the engine is in- 
tended. If a very equable motion is required, a heavier or 
swifter fly wheel must be employed. 

341. §.— What is Boulton and Watt's rule for fly wheels ? 
A, — Their rule is one which under any given circumstances 

fixes the sectional area of the fly wheel rim, and it is as fol- 



166 STRENGTHS OF CYLINDERS AND TRUNNIONS. 

lows : — multiply 44,000 times the square of the diameter of the 
cylinder in inches, by the length of the stroke in feet, and 
divide this product by the product of the square of the number 
of revolutions of the fly wheel per minute, multiplied by the 
cube of its diameter in feet. The quotient is the area of section 
of the fly wheel rim in square inches. 

STRENGTHS OF LAND ENGINES. 

342. Q, — Can you give a rule for telling the proper thickness 
of the cylinders of steam engines ? 

A. — In low pressure engines the thickness of metal of the 
cylinder, in engines of a medium size, should be about ^^th of 
the diameter of the cylinder, which, with a pressure of steam of 
20 lbs. above the atmosphere, will occasion a strain of only 
400 lbs. per square inch of section of the metal ; the thickness 
of the metal of the trunnion bearings of oscillating engines 
should be ^d of the diameter of the cylinder, and the breadth 
of the bearing should be about half its diameter. In high 
pressure engines the thickness of the cylinder should be 
about Y^th its diameter, which, with a pressure of steam of 
80 lbs. upon the square inch, will occasion a strain of 640 lbs. 
upon the square inch of section of the metal ; and the thickness 
of the metal of the trunnion bearings of high pressure oscil- 
lating engines should be Y^3th of the diameter of the cylinder. 
The strength, however, is not the sole consideration in propor- 
tioning cylinders, for they must be made of a certain thickness, 
however small the pressure is within them, that they may not 
be too fragile, and will stand boring. While, also, an engine 
of 40 inches diameter would be about one inch thick, the thick- 
ness would not be quite two inches in an 80 inch cylinder. In 
fact there will be a small constant added to the thickness for 
all diameters, which will be relatively larger the smaller the 
cylinders become. In the cylinders of Penn's 12 horse power 
engines, the diameter of cylinder being 21^ inches, the thick- 
ness of the metal is y^ths : in Penn's 40 inch cylinders, the 
thickness is 1 inch, and in the engines of the Ripon, Pottinger, 



* 



i 



STRENGTHS OF PISTON HOD, MAIN LINKS, ETC. 167 

and Indus, by Messrs. Miller, Eavenhill and Co., with cylinders 
76 inches diameter, the thickness of the metal is 1 j|. These are 
all oscillating engines. 

343. Q. — What is the proportion of the pistonjrod ? 

A. — The diameter of the piston rod is usually made y^^th of 
the diameter of the cylinder, or the sectional area of the piston 
rod is Y^th of the area of the cylinder. This proportion, how- 
ever, is not applicable to locomotive, or even fast moving marine 
engines. In locomotive engines the piston rod is made |th of 
the diameter of the cylinder, and it is obvious that where the 
pressure on the piston is great, the piston rod must be larger 
than when the pressure on the piston is small. 

344. Q. — What are the proper dimensions of the main links 
of a land beam engine ? 

A. — The sectional area of the main links in land beam en- 
gines is yy 3th of the area of the cylinder, and the length of the 
main links is usually half the length of the stroke. 

345. Q. — What are the dimensions of the connecting rod of 
a land engine ? 

A. — In land engines the connecting rod is usually of cast 
iron with a cruciform section : the breadth across the arms of 
the cross is about J^th of the length of the rod, the sectional 
area at the centre 2^^th of the area of the cylinder, and at the 
ends g^^th of the area of the cylinder : the length of the rod is 
usually 3 1 times the length of the stroke. It is preferable, how- 
ever, to make the connecting rod of malleable iron^ and then 
the dimensions will be those proper for marine engines. 

346. Q. — What was Mr. Watt's rule for the connecting rod ? 
A. — Some of his connecting rods were of iron and some of 

wood. To determine the thickness when of wood, multiply 
the square of the diameter of the cylinder in inches by the 
length of the stroke in feet, and divide the product by 24. 
Extract the fourth root of the quotient, which is the thickness 
In inches. For iron the rule is the same, only the divisor was 
57-6 instead of 24. 

347. Q. — What are the dimensions of the end studs of a, 
land engine beam ? 



168 STRENGTHS OF STUDS AND GUDGEONS. 

A. — In low pressure engines the diameter of the end studs 
of the engine beam are usually made ith of the diameter of the 
cylinder when of cast iron, and J^th when of TSTought iron, 
which gives * load with low steam of about 500 lbs. per circu- 
lar inch of transverse section ; but a larger size is preferable, as 
with large bearings the brasses do not wear so rapidly and the 
straps are not so likely to be burst by the bearings becoming 
oval. These sizes, as also those which immediately follow, sup- 
pose the pressure on the piston to be 18 lbs. per circular inch. 

348. Q. — How is the strength of a cast iron gudgeon com- 
puted ? 

A, — To find the proper size of a cast iron gudgeon adapted 
to sustain any given weight : — multiply the weight in lbs. by 
the intended length of bearing expressed in terms of the diame- 
ter ; divide the product by 500, and extract the square root of 
the quotient, which is the diameter in inches. 

349. §.— What was Mr. Watt's rule for the strength of 
gudgeons ? 

A. — Supposing the gudgeon to be square, then, to ascertain 
the thickness, multiply the weight resting on the gudgeon by 
the distance between the trunnions, and divide the product by 
333. Extract the cube root of the quotient, which is the thick- 
ness in inches. . 

350. Q. — How do you find the jproper strength for the cast 
iron beam of a land engine ? 

A. — If the force acting at the end of an engine beam be 
taken at 18 lbs. per circular inch of the piston, then the force 
acting at the middle will be 36 lbs. per circular* inch of the 
piston, and the proper strength of the beam at the centre will 
be found by the following rule : — divide the weight in lbs. act- 
ing at the centre by 250, and multiply the g[Uotient by the dis- 
tance between the extreme centres. To find the depth, the 
breadth being given : — divide this product by the breadth in 
inches, and extract the square root of the quotient, which is the 
depth. The depth of a land engine beam at the ends is usually 
made one third of the depth at the centre (the depth at the 
centre being equal to the diameter of the cylinder in the case 



STRENGTH OF CAST IRON SHAFTS. 169 

of low pressure engines), wMle the length is made equal to three 
times the length of the stroke, and the mean thickness fj^th of 
the length — the width of the edge bead being about three times 
the thickness of the web. In many modem engines the force 
acting at the end of the beam is more than 18 lbs. per circular 
inch of the piston, but the above rules are still applicable by- 
taking an imaginary cylinder with an area larger in the propor- 
tion of the larger pressure. 

351. Q. — What was Mr. Watt's rule for the main beams of 
his engines ? 

A. — Some of those beams were of wood and some of cast 
iron. The wood beams were so proportioned that the thick- 
ness was ^'^th of the circumference, and the depth ^.\j. The 
side of the beam, supposing it square, was found by multiply- 
ing the diameter of the cylinder by the length of the stroke, 
and extracting the cube root of the quotient, which will be the 
depth or thickness of the beam. This rule allows a beam 16 
feet long to bend ^th of an inch, and a beam 32 feet long to 
bend J of an inch. For cast iron beams the square of the 
diameter of the cylinder, multiplied by the length between the 
centres, is equal to the square of the depth, multiplied by the 
thickness. 

352. Q. — What law does the strength of beams and shafts 
follow ? 

A. — In the case of beams subjected to a breaking force, the 
strength with any given cohesion of the material will be pro- 
portional to the breadth, multiplied by the square of the depth ; 
and in the case of revolving shafts exposed to a twisting strain, 
the strength with any given cohesive power of the material will 
be as the cube of the diameter. 

353. Q. — How is the strength of a cast iron shaft to resist 
torsion determined ? 

A, — Experiments upon the force requisite to twist off cast 
iron necks show that if the cube of the diameter of neck in 
inches be multiplied by 880, the product will be the force of 
torsion which will twist them off when acting at 6 inches radi- 
us ; on this fact the following rule is founded : To find the di- 



170 PROPORTIONS PROPER FOR TEETH OF WHEELS. 



I 



ameter of a cast iron fly wheel shaft : — multiply the square of 
the diameter of the cylinder in inches, by the length of the 
crank in inches, and extract the cube root of the product, 
which multiply by 0*3025, and the result will be the proper 
diameter of the shaft in inches at the smallest part, when of 
cast iron. 

354. Q. — What was Mr. Watt's rule for the necks of his 
crank shafts ? 

A. — Taking the pressure on the piston at 12 lbs. pressure on 
the square inch, and supposing this force to be applied at one 
foot radius, divide the total pressure of the piston reduced to 1 
foot of radius by 31*4, and extract the cube root of the quotient, 
which is the diameter of the shaft : or extract the cube root of 
13-7 times the number of cubic feet of steam required to make 
one revolution, which is also the diameter of the shaft. 

355. Q. — Can you give any rule for the strength of the teeth 
of wheels ? 

A. — To find the proper dimensions for the teeth of a cast 
iron wheel : — multiply the diameter of the i3itch circle in feet 
by the number of revolutions to be made per minute, and re- 
serve the product for a divisor ; multiply the number of acUial 
horses power to be transmitted by 240, and divide the product 
by the above divisor, which will give the strength. If the 
pitch be given to find the breadth, divide the above strength by 
the square of the pitch in inches ; or if the breadth be giren, 
then to find the pitch divide the strength by the breadth in 
inches, and extract the square root of the quotient, which is the 
proper pitch in inches. The length of the teeth is usually 
about |ths of the pitch. Pinions to work satisfactorily should 
not have less than 30 or 40 teeth, and where the speed exceeds 
220 feet in the minute, the teeth of the larger wheel should be 
of wood, made a little thicker, to keep the strength unim- 
paired. 

356. ^.— Wliat was Mr. Watt's rule for the pitch of wheels ? 
A. — Multiply five times the diameter of the larger wheel l)y 

the diameter of the smaller, and extract the fourth root of th« 
product, which is the pitch. 



f 



CONNECTING AND SIDE KODS OF MAKINE ENGINES. 171 
BTRENGTn OF MARINE AND LOCOMOTIVE ENGINES. 

357. Q, — Cannot you give some rules of strength whicli will 
be applicable whatever pressure may be employed ? 

A. — In the rules already given, the effective pressure may be 
reckoned at from 18 to 20 lbs. upon every square inch of the 
piston, as is usual in land engines ; and if the pressure upon 
every square inch of the piston be made twice greater, the di- 
mensions must just be those proper for an engine of twice the 
area of piston. It will not be difSicult, however, to introduce 
the pressure into the rules as an element of the computation, 
whereby the result will be applicable both to high and low 
pressure engines. 

358. Q. — Will you apply this mode of computation to a ma- 
rine engine, and first find the diameter of the piston rod ? 

A, — The diameter of the piston rod may be found by multi- 
plying the diameter of the cylinder in inches, by the square 
root of the pressure on the piston in lbs. per square inch, and 
dividing by 50, which makes the strain |th of the elastic force. 

359. Q. — What will be the rule for the connecting rod, sup- 
posing it to be of malleable iron ? 

A. — The diameter of the connecting rod at the ends, may 
be found by multiplying 001 9 times the square root of the 
pressure on the piston in lbs. per square inch by the diameter 
of the cylinder in inches ; and the diameter of the connecting 
rod in the middle may be found by the following rule : — to 
00035 times the length of the connecting rod in inches, add 1, 
and multiply the sum by 0*019 times the square root of the 
pressure on the piston in lbs. per square incli, multiplied by the 
diameter of the cylinder in inches. The strain is equal to J-th 
of the elastic force. 

360. Q. — How will you find the diameter of the cylinder 
side rods of a marine engine ? 

A. — The diameter of the cylinder side rods at the ends may 
be found by multiplying 001 29 times the square root of the 
pressure on the piston in lbs. per square inch by the diameter 
of the cylinder ; and the diameter of the cylinder side rods at 



172 DIMENSIONS OF MALLEABLE IRON CRANKS. 

the middle is found by the following rule : — to 0*0035 times 
the length of the rod in inches, add 1, and multiply the sum 
by 0-0129 times the square root of the pressure on the piston in 
lbs. per square inch, multiplied by the diameter of the cylinder 
in inches ; the product is the diameter of each side rod at the 
centre in inches. The strain upon the side rods is by these 
rules equal to ^th of the elastic force. 

361. Q. — How do you determine the dimensions of the crank ? 
A. — To find the exterior diameter of the large eye of the 

crank when of malleable iron : — to 1*561 times the pressure of 
the steam upon the piston in lbs. per square inch, multiplied by 
the square of the length of the crank in inches, add 0*00494 
times the square of the diameter of the cylinder in inches, mul- 
tiplied by the square of the number of lbs. pressure per square 
inch on the piston ; extract the square root of this quantity ; 
divide the result by 75*59 times the square root of the length 
of the crank in inches, and multiply the quotient by the diam- 
eter of the cylinder in inches ; square the product and extract 
the cube root of the square, to which add the diameter of the 
hole for the reception of the shaft, and the result will be the 
exterior diameter of the large eye of the crank when of malle- 
able iron. The diameter of the small eye of the crank may be 
found by adding to the diameter of the crank pin 0*02521 
times the square root of the pressure on the piston in lbs. per 
square inch, multiplied by the diameter of the cylinder in 
inches. 

362. ^.— What will be the thickness of the crank web ? 

A. — The thickness of the web of the crank, supposing it to 
be continued to the centre of the shaft, would at that point be 
represented by the following rule : — to 1*561 times the square 
of the length of the crank in inches, add 0*00494 times the 
square of the diameter of the cylinder in inches, multiplied by 
the pressure on the piston in lbs. per square inch ; extract the 
square root of the sum, which multiply by the diameter of the 
cylinder squared in inches, and by the pressure on the piston 
in lbs. per square inch ; divide the product by 9,000, and ex- 
tract the cube root of the quotient, which will be the proper 



DIMENSIONS OF MALLEABLE IRON SHAFTS. 173 

thickness of the web of the crank when of malleable iron, sup- 
posing the web to be continued to the centre of the shaft. The 
thickness of the web at the crank pin centre, supposing it to be 
continued thither, would be 0*022 times the square root of the 
pressure on the piston in lbs. per square inch, multiplied by the 
diameter of the cylinder. The breadth of the web of the crank 
at the shaft centre should be twice the thickness, and at the 
pin centre 1| times the thickness of the web ; the length of the 
large eye of the crank would be equal to the diameter of the 
shaft, and of the small eye 0*0375 times the square root of the 
pressure on the piston in lbs. per square inch, multiplied by the 
diameter of the cylinder. 

363. Q. — Will you apply the same method of computation 
to find the dimensions of a malleable iron paddle shaft ? 

A, — The method of computation will be as follows : — to 
find the dimensions of a malleable iron paddle shaft, so that 
the strain shall not exceed |ths of the elastic force, or |ths 
of the force iron is capable of withstanding without permanent 
derangement of structure, which in tensile strains is taken at 
17,800 lbs. per square inch: multiply the .pressure in lbs. per 
square inch on the piston by the square of the diameter of the 
cylinder in inches, and the length of the crank in inches, and ex- 
tract the cube root of the product, which, multiplied by 0*08264, 
will be the diameter of the paddle shaft journal in inches when 
of malleable iron, whatever the pressure of the steam may be. 
The length of the paddle shaft journal should be 1 J times the 
diameter ; and the diameter of the part where the crank is put 
on is often made equal to the diameter over the collars of the * 
journal or bearing. 

364. Q. — How do you find the diameter oi the crank pin ? 
A, — The diameter of the crank pin in inches may be found 

by multiplying 0*02836 times the square root of the pressure on 
the piston in lbs. per square inch, by the diameter of the cylin- 
der in inches. The length of the pin is usually about fth times 
its diameter, and the strain if all thrown upon the end of tho 
pin will be equal to the elastic force ; but in ordinary working, 
the strain will only be equal to -Jd of the elastic force. 



174 DIMENSIONS OF CROSS HEAD AND MAIN CENTKE. 

305. Q. — Wliat are the dimensions of the cross head ? 

A. — If the length of the cross head be taken at 1'4 times 
the diameter of the cylinder, the dimensions of the cross head 
will be as follows : — the exterior diameter of the eye in the cross 
head for the reception of the piston rod, will be equal to the 
diameter of the hole, plus 002827 times the cube root of the 
pressure on the piston in lbs. per square inch, multiplied by the 
diameter of the cylinder in inches ; and the depth of the eye 
will be 0'0979 times the cube root of the pressure on the piston 
in lbs. per square inch, multiplied by the diameter of the cylin- 
der in inches. The diameter of each cross head journal will be 
0'01716 times the square root of the pressure on the piston in 
lbs. per square inch, multiplied by the diameter of the cylinder 
in inches — the length of the journal being ^ths its diameter. 
The thickness of the web at centre will be 0*0245 times the cube 
root of the pressure on the piston in lbs. per square inch, multi- 
plied by the diameter of the cylinder in inches ; and the depth 
of web at centre will be 0*09178 times the cube root of the jDres- 
sure on the jDiston in lbs. per square inch, multiplied by the 
diameter of the cylinder in inches. The thickness of the web 
at journal will be 0*0122 times the square root of the pressure 
on the piston in lbs. per square inch, multiplied by the diam- 
eter of the cylinder in inches ; and the depth of the web at 
journal will be 0*0203 times the square root of the pressure 
upon the piston in lbs. per square inch, multiplied by the di- 
ameter of the cylinder in inches. In these rules for the cross 
head, the strain upon the web is -ohj times the elastic force ; 
•the strain upon the journal in ordinary working is 2 Vj times 
the elastic force ; and if the outer ends of the journals are the 
only bearing points, the strain is ^.^-^^^ times the elastic force, 
which is very little in excess of the elastic force. 

366. Q. — How do you find the diameter of the main centre 
when proportioned according to this rule ? 

A. — The diameter of the main centre may be found by mul- 
tiplying 00367 times the square root of the j^rcssure upon the 
piston in lbs. per square inch, by the diameter of the cylinder in 
inches, which will give the diameter of the main centre journal 



f 



DIMENSIONS OF GIBS AND CUTTERS. 175 

in inches when of malleable iron, and the length of the main 
centre journal should be 1^ times its diameter ; the strain upon 
the main centre journal in ordinary working will be about ^ the 
elastic force. 

367. Q. — What are the proper dimensions of the gibs and 
cutters of an engine ? 

A. — The depth of gibs and cutters for attaching the piston 
rod to the cross head, is 0358 times the cube root of the pres- 
sure of the steam on the piston in lbs. per square inch, multi- 
plied by the diameter of the cylinder ; and the thickness of the 
gibs and cutters is 0*007 times the cube root of the pressure on 
the piston in lbs. per square inch, multiplied by the diameter 
of its cylinder. The depth of the cutter through the piston is 
017 times the square root of the pressure on the piston in lbs. 
per square inch, multiplied by the diameter of the cylinder in 
inches ; and the thickness of the cutter through the piston is 
0*007 times the square root of the pressure on the piston in lbs. 
per square inch, multiplied by the diameter of the cylinder. 

368. Q, — Are not some of the parts of an engine constructed 
according to these rules too weak, when compared with the 
other parts ? 

A, — It is obvious, from the varying proportions subsisting 
in the different parts of the engine between the strain and the 
elastic force, that in engines proportioned by these rules — which 
represent nevertheless the average practice of the best construct- 
ors — some of the parts must possess a considerable excess of 
strength over other parts, and it appears expedient that this 
disparity should be diminished, which may best be done by in- 
creasing the strength of the parts which are weakest ; inasmuch 
as the frequent fracture of some of the parts shows that the di- 
mensions at present adopted for those parts are scarcely suffi- 
cient, unless the iron of which they are made is of the best 
quality. At the same time it is quite certain, that engines pro- 
portioned by these rules will work satisfactorily where good ma- 
terials are employed ; but it is important to know in what parts 
good materials and larger dimensions are the most indispens- 
able. In many of the parts, moreover, it is necessary that the 



176 PARTS SHOULD BE LARGE FOR WEAR. 

dimensions should be proportioned to meet tlie wear and the 
tendency to heat, instead of being merely proportioned to ob- 
tain the necessary strength ; and the crank pin is one of the 
parts which requires to be large in diameter, and as long as 
possible in the bearing, so as to distribute the pressure, and 
prevent the disposition to heat which would otherwise exist. 
The cross head journals also should be long and large ; for as 
the tops of the side rods have little travel, the oil is less 
drawn into the bearings than if the travel was greater, and is 
being constantly pressed out by the punching strain. This 
strain should therefore be reduced as far as possible by its dis- 
tribution over a large surface. In the rules which are contained 
in the answers to the ten preceding questions (358 to 367) the 
pressure on the piston in lbs. per square inch is taken as the 
sum of the pressure of steam in the boiler and of the vacuum ; 
the latter being assumed to be 15 lbs. per square inch. 



CHAPTER Vn. 

CONSTRUCTIVE DETAILS OF BOILERS. 



LAND AND MARINE BOILERS. 

369. Q, — Will you explain the course of procedure in tlie 
construction and setting of wagon boilers ? 

A, — Most boilers are made of plates three eighths of an inch 
thick, and the rivets are from three eighths to three fourths of 
an inch in diameter. In the bottom and sides of a wagon boil- 
er the heads of the rivets, or the ends formed on the rivets be- 
fore they are inserted, should be large and placed next the fire, 
or on the outside ; whereas on the top of the boiler the heads 
should be on the inside. The rivets should be placed about 
two inches distant from centre to centre, and the centre of the 
row of rivets should be about one inch from the edge of the 
plate. The edges of the plates should be truly cut, both inside 
and outside, and after the parts of the boiler have been riveted 
together, the edges of the plates should be set up or caulked 
with a blunt chisel about a quarter of an inch thick in the 
point, and struck by a hammer of aoout three or four pounds 
weight, one man holding the caulking tool while another 
strikes. 

370. (2.— Is this the usual mode of caulking ? 



178 MODE OF CONSTRUCTING LAND BOILERS. 

A. — No, it is not the usual mode ; but it is the best mode, 
and is the mode adopted by Mr. Watt. The usual mode now 
is for one man to caulk the seams with a hammer in one hand 
and a caulking chisel in the other, and in some of the difficult 
corners of marine flue boilers it is not easy for two men to get 
in. A good deal of the caulking has also sometimes to be done 
with the left hand. 

371. ^.—Should the boiler be proved after caulking ? 
^.— The boiler should be filled with water and caulked 

afresh in any leaky part. When emptied again, all the joints 
should be painted with a solution of sal ammoniac in urine, 
and' so soon as the seams are well rusted they should be dried 
with a gentle fire, and then be painted over with a thin putty 
formed of whiting and linseed oil, the heat being continued 
until the putty becomes so hard that it cannot be readily 
scratched with the nail, and care must be taken neither to burn 
the putty nor to discontinue the fire until it has become quite 
dry. 

372. Q. — How should the brickwork setting of a wagon 
boiler be built ? 

A. — In building the brickwork for the setting of the boiler, 
the part upon which the heat acts with most intensity is to be 
built with clay instead of mortar, but mortar is to be used on 
the outside of the work. Old bars of flat iron may be laid 
under the boiler chime to prevent that part of the boiler from 
being burned out, and bars of iron should also run through the 
brickwork to prevent it from splitting. The top of the boiler 
is to be covered with brickwork laid in the best lime, and if the 
lime be not of the hydraulic kind, it should be mixed with 
Dutch terrass, to make it impenetrable to water. The top of 
the boiler should be well plastered with this lime, which will 
greatly conduce to the tightness of the seams. Openings into 
the flues must be left in convenient situations to enable the 
flues to be swept out when required, and these openings may be 
closed with cast iron doors jointed with clay or mortar, which 
may be easily removed when required. Adjacent to the chim- 
ney a slit must be left in the top of the flue with a groove in 



MODE OF CONSTRUCTING MARINE BOILERS. 179 

the brickwork to enable the sliding door or damper to be fixed 
in that situation, which by being lowered into the flue will 
obstruct the passage of the smoke and moderate the draught, 
whereby the chimney will be prevented from drawing the flame 
into it before the heat has acted sufficiently upon the boiler. 

373. Q. — Are marine constructed in the same way as land 
boilers ? 

A. — There is very little difference in the two cases : the 
whole of the shells of marine boilers, however, should be double 
riveted with rivets f gths of an inch in diameter, and 2^th inch- 
es from centre to centre, the weakening effect of double riv- 
eting being much less than that of single riveting. The fur- 
naces above the line of bars should be of the best Lowmoor, 
Bowling, or Staffordshire scrap plates, and the portion of each 
furnace above the bars should consist only of three plates, one 
for the top and one for each side, the lower seam of the side 
plates being situated beneath the level of the bars, so as not to 
be exposed to the heat of the furnace. The tube plates of tu- 
bular boilers should be of the best Lowmoor, or Bowling iron, 
seven eighths to one inch thick : the shells should be of the 
best Staffordshire, or Thornycroft S crown iron f'gths of an inch 
thick. 

374. Q. — Of what kind of iron should the angle iron or cor- 
ner iron be composed ? 

A. — Angle iron should not be used in the construction of 
boilers, as in the manufacture it becomes reedy, and is apt to 
split up in the direction of its length : it is much the safer 
practice to bend the plates at the corners of the boiler ; but this 
must be carefully done, without introducing any more sharp 
bends than can be avoided, and plates which require to be bent 
much should be of Lowmoor iron. It will usually be found ex- 
pedient to introduce a ring of angle iron around the furnace 
mouths, though it is discarded in the other parts of the boiler ; 
but it should be used as sparingly as possible, and any that is 
used should be of the best quality. 

375. Q. — Is it not important to have the holes in the plates 
opposite to one another ? 



180 HOW TO SET BOILERS IN WOODEN SHIPS. 

A. — The whole of the plates of a boiler should have the 
holes for the rivets punched, and the edges cut straight, by 
means of self-acting machinery, in which a travelling table car- 
ries forward the plate with an equal progression every stroke 
of the punch or shears ; and machinery of this kind is now ex- 
tensively employed. The practice of forcing the parts of boil- 
ers together with violence, by means of screw-jacks, and drifts 
through the holes, should not be permitted ; as a great strain 
may thus be thrown upon the rivets, even when there is no 
steam in the boiler. All rivets sluould be of the best Lowmoor 
iron. The work should be caulked both within and without 
wherever it is accessible, but in the more confined situations 
within the flues the caulking will in many cases have to be 
done with the hand or chipping hammer, instead of the heavy 
hammer previously prescribed. 

376. Q. — How is the setting of marine boilers with internal 
furnaces effected ? 

A. — In the setting of marine boilers care must be taken that 
no copper bolts or nails project above the wooden platform 
upon which they rest, and also that no projecting copper bolts 
in the sides of the ship touch the boiler, as the galvanic action 
in such a case would probably soon wear the points of contact 
into holes. The platform may consist of three inch planking 
laid across the keelsons nailed with iron nails, the heads of 
which are well punched down, and caulked and puttied like a 
deck. The surface may then be painted over with thin putty, 
and fore and aft boards of half the thickness may then be laid 
down and nailed securely with iron nails, having the heads 
well punched down. This platform must then be covered thinly 
and evenly with mastic cement and the boiler be set down upon 
it, and the cement must be caulked beneath the boiler by means 
of wooden caulking tools, so as completely to fill every vacuity. 
Coomings of wood sloped on the top must next be set round the 
boiler, and the space between the coomings and the boiler must 
be caulked full of cement, and be smoothed off on the top to 
the slope of the coomings, so as to throw off any water that 
might be disposed to enter between the coomings and the boiler. 



CEMENT PROPER FOR SETTING BOILERS. 181 

377. Q. — How is the cement used for setting marine boilers 
\^^ Compounded ? 

^.—Mastic cement proper for the setting of boilers is sold 
in many places ready made. Hamelin's mastic is compounded 
as follows :— to any given weight of sand or pulverized earthen- 
ware add two thirds such given weight of powdered Bath, Port- 
land, or other similar stone, and to every 560 lbs. weight of the 
mixture add 40 lbs. weight of litharge, 2 lbs. of powdered gla^s 
or flint, 1 lb. of minium, and 2 lbs. of gray oxide of lead ; pass 
the mixture through a sieve, and keep it in a powder for use. 
When wanted for use, a sufficient quantity of the powder is 
mixed with some vegetable oil upon a board or in a trough in 
the manner of mortar, in the proportion of 605 lbs. of the pow- 
der to 5 gallons of linseed, walnut, or pink oil, and the mixture 
is stirred and trodden upon until it assumes the appearance of 
moistened sand, when it is ready for use. The cement should 
be used on the same day as the oil is added, else it will be set 
into a solid mass. 

378. §. — What is the best length of the furnaces of marine 
boilers ? 

A. — It has already been stated that furnace bars should not 
much exceed six feet in length, as it is difficult to manage long- 
furnaces ; but it is a frequent practice to make the furnaces 
long and narrow, the consequence of which is, that it is impos- 
sible to fire them effectually at the after end, especially upon 
long voyages and in stormy weather, and air escapes into the 
flues at the after end of the bars, whereby the efficacy of the 
boiler is diminished. Where the bars are very long it will 
generally be found that an increased supply of steam and a 
diminished consumption of coal will be the consequence of 
shortening them, and the bars should always lie with a consid- 
erable inclination to facilitate the distribution of the fuel over 
the after part of the furnace. When there are two lengths of 
bars in the furnace, it is expedient to make the central cross 
bar for bearing up the ends double, and to leave a space be- 
tween the ends of the bars so that the ashes may fall through 
between them. The space thus left enables the bars to expand 
9 



182 FOEMATION AND ADVANTAGES OF BRIDGES. 

without injury on the application of heat, whereas without some 
such provision the bars are very liable to get burned out by 
bending up in the centre, or at the ends, as they must do if the 
elongation of the bars on the application of heat be prevented ; 
and this must be the effect of permitting the spaces at the ends 
of the bars to be filled up with ashes. At each end of each bed 
of bars it is expedient to leave a space which the ashes cannot 
fill up so as to cause the bars to jam ; and care must be taken 
that the heels of the bars do not come against any of the fur- 
nace bearers, whereby the room left at the end of the bars to per- 
mit the expansion would be rendered of no avail. 

379. Q. — Have you any remarks to offer respecting the con- 
struction and arrangement of the furnace bridges and dampers 
of marine boilers ? 

A. — The furnace bridges of marine boilers are walls or par- 
titions built up at the ends of the furnaces to narrow the open- 
ing for the escape of heat into the flues. They are either made 
of fire brick or of plate iron containing water : in the case of 
water bridges, the top part of the bridge should be made with 
a large amount of slant so as to enable the steam to escape 
freely, but notwithstanding this precaution the plates of water 
bridges are apt to crack at the bend, so that fire brick bridges 
appear on the whole to be preferable. In shallow furnaces the 
bridges often come too near the furnace top to enable a man to 
pass over them ; and it will save expense if in such bridges the 
upper portion is constructed of two or three fire blocks, which 
may be lifted off where a person requires to enter the flues to 
sweep or repair them, whereby the perpetual demolition and 
reconstruction of the upper part of the bridge will be pre- 
vented. 

380. C.— What is the benefit of bridges ? 

A. — Bridges are found in practice to have a very sensible 
operation in increasing the production of steam, and in some 
boilers in which the brick bridges have been accidentally 
knocked down by the firemen, a very considerable diminution 
in the supply of steam has been experienced. Their chief oper- 
ation seems to lie in concentrating the heat within the furnace 



USES OF HANGING BRIDGES. 183 

to a Mglier temperature, whereby the heat is more rapidly trans- 
mitted from the furnace to the water, and less heat has conse- 
quently to be absorbed by the flues. In this way the bridges 
render the heating surface of a boiler more effective, or enable a 
smaller amount of heating surface to suffice. 

381. Q. — Are the bridges behind the furnaces the only 
bridges used in steam boilers ? 

A, — It is not an uncommon practice to place a hanging 
bridge, consisting of a plate of iron descending a certain dis- 
tance into the flue, at that part of the flue where it enters the 
chimney, whereby the stratum of hot air which occupies the 
highest part of the flue is kept in protracted contact with the 
boiler, and the cooler air occupying the lower part of the flue is 
that which alone escapes. The practice of introducing a hanging 
bridge is a beneficial one in the case of some boilers, but is not 
applicable universally, as boilers with a small calorimeter can- 
not be further contracted in the flue without a diminution in 
their evaporating power. In tubular boilers a hanging bridge 
is not applicable, but in some cases a perforated plate is placed 
against the ends of the tubes, which by suitable connections is 
made to operate as a sliding damper which partially or totally 
closes up the end of every tube, and at other times a damper 
constructed in the manner of a Venetian blind is employed in 
the same situation. These varieties of damper, however, have 
only yet been used in locomotive boilers, though applicable to 
tubular boilers of every description. 

382. Q. — Is it a benefit to keep the flues or tubes apper- 
taining to each furnace distinct ? 

A. — In a flue boiler this cannot be done, but in a tubular 
boiler it is an advantage that there should be a division be- 
tween the tubes pertaining to each furnace, so that the smoke 
of each furnace may be kept apart from the smoke of the fur- 
nace adjoining it until the smoke of both enters the chimney, 
as by this arrangement a furnace only will be rendered inopera- 
tive in cleaning the fires instead of a boiler, and the tubes be- 
longing to one furnace may be swept if necessary at sea with- 
out interfering injuriously with the action of the rest. In a 



184 HOW TO PREYENT FURNACES FROM BURNING. 

steam vessel it is necessary at intervals to empty out one or 
more furnaces every watch to get rid of the clinkers which 
would otherwise accumulate in them ; and it is advisable that 
the connection between the furnaces should be such that this 
operation, when being performed on one furnace, shall injure the 
action of the rest as little as possible. 

383. Q. — Can any constructive precautions be taken to pre- 
vent the furnaces and tube plates of the boiler from being 
burned by the intensity of the heat ? 

A. — The sides of the internal furnaces or flues in all boilers 
should be so constructed that the steam may readily escape 
from their surfaces, with which view it is expedient to make 
the bottom of the flue somewhat wider than the top, or slightly 
conical in the cross section ; and the upper plates should always 
be overlapped by the plates beneath, so that the steam cannot 
be retained in the overlap, but will escape as soon as it is gen- 
erated. If the sides of the furnace be made high and perfectly 
vertical, they will speedily be buckled and cracked by the heat, 
as a film of steam in such a case will remain in contact with 
the iron which will prevent the access of the water, and the iron 
of the boiler will be injured by the high temperature it must in 
that case acquire. To moderate the intensity of the heat acting 
upon the furnace sides, it is expedient to bring the outside fire 
bars into close contact with the sides of the furnace, so as to 
prevent the entrance of air through the fire in that situation, by 
which the intensity of the heat would be increased. The tube 
plate nearest the furnace in tubular boilers should also be so in- 
clined as to facilitate the escape of the steam ; and the short 
bent plate or flange of the tube plate, connecting the tube plate 
with the top of the furnace, should be made with a gradual 
bend, as, if the bend be sudden, the iron will be apt to crack 
or burn away from the concretion of salt. Where the furnace 
mouths are contracted by bending in the sides and top of the 
furnace, as is the general practice, the bends should be gradual, 
as salt is apt to accumulate in the pockets made by a sudden 
bend, and the plates will then bum into holes. 

384. Q.—hi what manner is the tubing of boilers performed ? 



MODE OP TUBING BOILERS AND STAYING TUBE PLATES. 185 

A. — The tubes of marine boilers are generally iron tubes, 
three inches in diameter, and between six and seven feet Ion 2: : 
but sometimes brass tubes of similar dimensions are employed. 
When" brass tubes are employed, the use of ferules driven into 
the ends of the tubes is sometimes employed to keep them 
tight ; but when the tubes are of malleable iron, of the thick- 
ness of Russell's boiler tubes, they may be made tight merely 
by firmly driving them into the tube plates, and the same may be 
done with thick brass tubes. The holes in the tube plate next 
the front of the boiler are just sensibly larger in diameter than 
the holes in the other tube plate, and the holes upon the outer 
surfaces of both tube plates are very slightly countersunk. The 
whole of the tubes are driven through both tube plates from 
the front of the boiler, — the precaution, however, being taken 
to drive them in gently at first with a light hand hammer, until 
tjie whole of the tubes have been inserted to an equal depth, 
and then they may be driven up by degrees with a heavy ham- 
mer, whereby any distortion of the holes from unequal driving 
will be prevented. Finally, the ends of the tubes should be 
riveted up so as to fill the countersink ; the tubes should be 
left a little longer than the distance between the outer surfaces 
of the tube plates, so that the countersink at the ends may be 
filled by staving up the end of the tube rather than by riveting 
it over ; and the staving will be best accomplished by means 
of a mandril with a collar upon it, which is driven into the 
tube so that the collar rests upon the end of the tube to be 
riveted ; or a tool like a blunt chisel with a recess in its point 
may be used, as is the more usual practice. 

385. Q. — Should not stays be introduced in substitution of 
some of the tubes ? 

A. — ^It appears expedient in all cases that some of the tubes 
should be screwed at the ends, so as to serve as stays if the riv- 
eting at the tube ends happens to be burned away, and also to 
act as abutments to the riveted tube — or else to introduce very 
strong rods of about the same diameter as a tube, in substitu- 
tion of some of the tubes ; and these stays should have nuts at 
each end both within and without the tube plates, which nuts 



186 PROPER MODE OF CONSTRUCTING THE CHIMNEY. 

should be screwed up, with white lead interposed, before the 
tubes are inserted. If the tubes are long, their expansion when 
the boiler is being blown off will be apt to start them at the 
^ends, unless very securely fixed ; and it is difficult to prevent 
brass tubes of large diameter and proportionate length from 
being started at the ends, even when secured by ferules ; but 
the brass tubes commonly employed are so small as to be suscep- 
tible of sufficient compression endways by the adhesion due to 
the ferules to compensate for the expansion, whereby they are 
prevented from starting at the ends. In some of the early ma- 
rine boilers fitted with brass tubes, a galvanic action at the ends 
of the tubes was found to take place, and the iron of the tube 
plates was wasted away in consequence, with rajjidity; but 
further experience proved the injury to be attributable chiefly 
to imperfect fitting, whereby a leakage was caused that induced 
oxidation, and when the tubes were well fitted any injurious 
action at the ends of the tubes was found to cease. 

386. Q. — What is the best mode of constructing the chim- 
ney and the parts in connection therewith ? 

A. — In sea-going steamers the funnel plates are usually 
about nine feet long and f\ths thick ; and where different flues 
or boilers have their debouch in the same chimney, it is expe- 
dient to run division plates up the chimney for a considerable 
distance, to keep the draughts distinct. The dampers should 
not be in the chimney but at the end of the boiler flue, so that 
they may be available for use if the funnel by accident be car- 
ried away. The waste steam pipe should be of the same height 
as the funnel, so as to carry the waste steam clear of it, for if 
the waste steam strikes the funnel it will wear the iron into 
holes ; and the waste steam pipes should be made at the bottom 
with a faucet joint, to prevent the working of the funnel, when 
the vessel rolls, from breaking the pipe at the neck. There 
should be two hoops round the funnel, for the attachment of 
the funnel shrouds, instead of one, so that the funnel may not 
be carried overboard if one hoop breaks, or if the funnel breaks 
at the upper hoop from the corrosive action of the waste steam, 
as sometimes happens. The deck over the steam chest should 



TELESCOPE CHIMNEYS AND MISCELLANEOUS DETAILS. 187 

be formed of an iron plate supported by angle iron beams, and 
there should be a high angle iron cooming round the hole in 
the deck through which the chimney ascends, to prevent any 
water upon the deck from leaking down upon the boiler. 
Around the lower part of the funnel there should be a sheet 
iron casing to prevent any inconvenient dispersion of heat in 
that situation, and another short piece of casing, of a somewhat 
larger diameter, and riveted to the chimney, should descend 
over the first casing, so as to prevent the rain or spray which 
may beat against the chimney from being poured down within 
the casing upon the top of the boiler. The pipe for conducting 
away the waste water from the top of the safety valve should 
lead overboard, and not into the bilge of the ship, as inconve- 
nience arises from the steam occasionally passing through it, if 
it has its termination in the engine room. 

387. Q, — Are not the chimneys of some vessels made so that 
they may be lowered when required ? 

A, — The chimneys of small river vessels which have to pass 
under bridges are generally formed with a hinge, so that they 
may be lowered backward when passing under a bridge ; and 
the chimneys of some screw vessels are made so as to shut up 
like a spyglass when the fires are put out and the vessel is navi- 
gated under sails. In smaller vessels, however, two lengths of 
chimney suffice ; and in that case there is a standing piece on 
deck, which, however, does not project above the bulwarks. 

388. §. — Will you explain any further details in the con- 
struction of marine boilers which occur to you as important ? 

A, — The man-hole and mud-hole doors, unless put on from 
the outside, like a cylinder cover, with a great number of bolts, 
should be put on from the inside with cross bars on the outside, 
and the bolts should be strong, and have coarse threads and 
square nuts, so that the threads may not be overrun, nor the 
nuts become round, by the unskilful manipulations of the fire- 
men, by whom these doors are removed or replaced. It is very 
expedient that sufficient space should be left between the fur- 
nace and the tubes in all tubular boilers to permit a boy to go 
in to clear away any scale that may have formed, and tg hold 



188 FOKMATION OF SCALE IN MARINE BOILERS. 

on the rivets in the event of repair being wanted ; and it is also 
expedient that a vertical row of tubes should be left out oppo- 
site to each water space to allow the ascent of the steam and 
descent of the water, as it has been found that the removal 
of the tubes in that position, even in a boiler with deficient 
heating surface, has increased the production of steam, and 
diminished the consumption of fuel. The tubes should all be 
kept in the same vertical line, so as to permit the introduction 
of an instrument to scrape them ; but they may be zig-zagged 
in the horizontal line, whereby a greater strength of metal will 
be obtained around the holes in the tube plates, and the tubes 
should not be placed too close together, else their heating effi- 
cacy will be impaired. 

IXCEUSTATION AND COEROSION OF BOILERS. 

389. Q. — What is the cause of the formation of scale in ma- 
rine boilers ? 

A, — Scale is formed in all boilers which contain earthy or 
saline matters, just in the way in which a scaly deposit, or rock, 
as it is sometimes termed, is formed in a tea kettle. In sea 
water the chief ingredient is common salt, which exists in solu- 
tion : the water admitted to the boiler is taken away in the 
shape of steam, and the saline matter which is not vaporizable 
accumulates in process of time in the boiler, until its amount is 
so great that the water is saturated, or unable to hold any more 
in solution ; the salt is then precipitated and forms a deposit 
which hardens by heat. The formation of scale, therefore, is 
similar to the process of making salt from sea water by evapor- 
ation, the boiler being, in fact, a large salt pan. 

390. Q, — But is the scale soluble in fresh water like the salt 
in a salt pan ? 

A. — No, it is not ; or if soluble at all, is only so to a very 
limited extent. The several ingredients in sea water begin to 
be precipitated from solution at different degrees of concentra- 
tion ; and tfee sulphate and carbonate of lime, which begin to 
be precipitated when a certain state of concentration is reached, 



A 



INCONVENIENCES OF SUCH INCRUSTATIONS. 189 

enter largely into the composition of scale, and give it its inso- 
luble character. Pieces of waste or other similar objects left 
within a marine boiler appear, when taken out, as if they had 
been petrified; and the scale deposited upon the flues of a 
marine boiler resembles layers of stone. 

391. Q. — Is much inconvenience experienced in marine 
boilers from these incrustations upon the flues ? 

^.—Incrustation in boilers at one time caused much more 
perplexity than it does at present, as it was supposed that in 
some seas it was impossible to prevent the boilers of a steamer 
from becoming salted up ; but it has now been satisfactorily 
ascertained that there is very little difference in the saltness of 
different seas, and that however salt the water may be, the 
boiler will be preserved from any injurious amount of incrusta- 
tion by blowing off, as it is called, very frequently, or by jjer- 
mitting a considerable portion of the supersalted water to 
escape at short intervals into the sea. If blowing off be 
sufficiently practised, the scale upon the flues will never be 
much thicker than a sheet of writing paper, and no excuse should 
be accepted from engineers for permitting a boiler to be dam- 
aged by the accumulation of calcareous deposit. 

393. Q. — What is the temperature at which sea water boils 
in a steam boiler ? 

A. — Sea water contains about J^rd its weight of salt, and in 
the open air it boils at the temperature of 213*2°; if the pro- 
portion of salt be increased to /grds of the weight of the water, 
the boiling point will rise to 214*4° ; with /^rds of salt the 
boiling point will be 215*5°; /grds, 216*7° ; g^ds, 217*9° ; g^ds, 
219°; gVds, 220*2°; |rds, 221*4° ; gV'ds, 222*5°; -Jfrds, 223*7° ; 
iirds, 224*9 °; and ^^f rds, which is the point of saturation, 226°. 
In a steam boiler the boiling points of water containing these 
proportions of salt must be higher, as the elevation of temper- 
ature due to the pressure of the steam has to be added to that 
due to the saltness of the water ; the temperature of steam at 
the atmospheric pressure being 212°, its temperature, at a pres- 
sure of 15 lbs. per square inch above the atmosphere, will be 
250°, and adding to this 4*7° as the increased temperature due 



190 MODE OF ESTIMATIXG SALTNESS. 



to the saltness of the water when it contains g^rds of salt, we 
have 254-7° as the temperature of the water in the boiler, when 
it contains 3'*3rds of salt and the pressure of the steam is 15 lbs. 
on the square inch. 

393. Q, — What degree of concentration of the salt water 
may be safely permitted in a boiler ? 

A. — It is found by experience that when the concentration 
of the salt water in a boiler is prevented from exceeding that 
point at which it contains /grds its weight of salt, no injurious 
incrustation will take place, and as sea water contains only -g^grd 
of its weight of salt, it is clear that it must be reduced by 
evaporation to one half of its bulk before it can contain g^grds 
of salt ; or, in other words, a boiler must blow out into the sea 
one half of the water it receives as feed, in order to prevent the 
water from rising above /grds of concentration, or 8 ounces of 
salt to the gallon. 

394. Q. — How do you determine 8 ounces to the gallon to 
be equivalent to twice the density of salt water, or " two salt 
waters " as it is sometimes called ? 

A. — The density of the water of difierent seas varies some- 
what. A gallon of fresh water weighs 10 lbs. ; a gallon of salt 
water from the Baltic weighs 10-15 lbs. ; a gallon of salt water 
from the Irish Channel weighs 10'28 lbs. ; and a gallon of salt 
water from the Mediterranean 10-29 lbs. If we take an average 
saltness represented by a weight of 10*25 lbs., then a gallon of 
water concentrated to twice this saltness will weigh 10-5 lbs., 
or the salt in it will weigh -5 lbs or 8 oz., which is the propor- 
tion of 8 oz. to the gallon. However, the proportion of /grds 
gives a greater proportion than 8 oz. to the gallon, for 3^3 = -,V 
nearly, and ^ of 10 lbs. =10 oz. By keeping the density of 
the water in a marine boiler at the proportion of 8 or 10 oz. to 
the gallon, no inconvenient amount of scale will be deposited 
on the flues or tubes. The bulk of water, it may be remarked, 
is not increased by putting salt in it up to the point of satura- 
tion, but only its density is increased. 

395. Q. — Is there not a great loss of heat by blowing off so 
large a proportion of the heated water from the boiler ? 



^ 



AMOUNT OF HEAT LOST BY BLOWING OFF. 191 

A.— The loss is not very great. Boilers are sometimes 
worked at a saltness of g^rds, and taking this saltness and sup- 
posing the latent heat of steam to be at 1000° at the tempera- 
ture of 21 2"^, and reckoning the sum of the latent and sensible 
heats as forming a constant quantity, the latent heat of steam 
at the temperature of 250° will be 962°, and the total heat of 
the steam will be 1212"^ in the case of fresh water; but as the 
feed water is sent into the boiler at the temperature of 100^, 
the accession of heat it receives from the fuel will be 1112° in 
the case of fresh water, or 1112° increased by 3-98° in the case 
of water containing g^rds of salt — the 3'98° being the 4*7° in- 
crease of temperature due to the presence of g^rds of salt, mul- 
tiplied by 0*847 the specific heat of steam. This makes the 
total accession of heat received by the steam in the boiler equal 
to 1115*98°, or say 1116°, w^hich multiplied by 3, as 3 parts of 
the water are raised into steam, gives us 3348° for the heat in 
the steam, while the accession of heat received in the boiler by 
the 1 part of residual brine will be 154*7°, multiplied by 0*85, 
the specific heat of the brine, or 130*495° ; and 3348° divided 
by 130*495^ is about o^h. It appears, therefore, that by blow- 
ing off the boiler to such an extent that the saltness shall not 
rise above what answers to /g.rds of salt, about gV^h of the heat 
is blown into the sea; this is but a small proportion, and as 
there will be a greater waste of heat, if from the existence of 
scale upon the flues the heat can be only imperfectly transmitted 
to the water, there cannot be even an economy of fuel in nig- 
gard blowing off, while it involves the introduction of other 
evils. ".The proportion of /grds of saltness, however, or 16 oz. 
to the gallon, is larger than is advisable, especially as it is 
difficult to keep the saltness at a perfectly uniform point, and 
the working point should, therefore, be 3^3 rds as before pre- 
scribed. 

396. Q. — Have no means been devised for turning to ac- 
count the heat contained in the brine which is expelled from 
the boiler ? 

A. — To save a jjart of the heat lost by the operation of 
blowing off, the hot brine is sometimes passed through a num- 



192 USUAL MODES OF BLOWING OFF. 

ber of small tubes surrounded by tlie feed water ; but tliere is 
no very great gain from tbe use of such apparatus, and the 
tubes are apt to become choked up, whereby the safety of the 
boiler may be endangered by the injurious concentration of its 
contents. Pumps, worked by the engine for the extraction of 
the brine, are generally used in connection with the small tubes 
for the extraction of the heat from the supersalted water ; and 
if the tubes become choked the pumps will cease to eject the 
water, while the engineer may consider them to be all the 
while in operation. 

397. Q. — What is the usual mode of blowing off the super- 
salted water from the boiler ? 

A. — The general mode of blowing off the boiler is to allow 
the water to rise gradually for an hour or two above the lowest 
working level, and then to open the cock communicating with 
the sea, and keep it open until the surface of the water within 
the boiler has fallen several inches ; but in some cases a cock 
of smaller size is allowed to run water continuously, and in 
other cases brine pumps are used as already mentioned. In 
every case in which the supersalted water is discharged from 
the boiler in a continuous stream, a hydrometer or salt gauge 
of some convenient construction should be applied to the boiler^ 
so that the density of the water may at all times be visible, and 
immediate notice be given of any interruption of the operation. 
Various contrivances have been devised for this purpose, the 
most of which operate on the principle of a hydrometer ; but 
perhaps a more satisfactory principle would be that of a differ- 
ential steam gauge, which would indicate the differepce of 
pressure between the steam in the boiler and the steam of a 
small quantity of fresh water enclosed in a suitable vessel, and 
immerged in the water of the boiler. 

398. Q. — What is the advantage of blowing off from the 
surface of the water in the boiler ? 

A, — Blowing off from a point near the surface of the water 
is more beneficial than blowing off from the bottom of the 
boiler. Solid particles of any kind, it is well known, if intro- 
duced into boiling water, will lower the boiling point in a slight 



LAMBS SCALE PREVENTER. 193 

degree, and the steam will cliiefly be generated on the surface 
of the particles, and indeed will have the appearance of coming 
out of them ; if the particles be small the steam generated 
beneath and around them will balloon them to the surface of 
the water, where the steam will be liberated and the particles 
will descend ; and the impalpable particles in a marine boiler, 
which by their subsidence upon the flues concrete into scale, are 
carried in the first instance to the surface of the water, so that 
if they be caught there and ejected from the boiler, the forma- 
tion of scale will be prevented. 

399. Q, — Are there any plans in operation for taking ad- 
vantage of this property of particles rising to the surface ? 

A, — Advantage is taken of this property in Lamb's Scale 
Preventer, which is substantially a contrivance for blowing off 
from the surface of the water that in practice is found to be 
very effectual ; but a float in connection with a valve at the 
mouth of the discharging pipe is there introduced, so as to 
regulate the quantity of water blown out by the height of the 
water level, or by the extent of opening given to the feed cock. 
The operation, however, of the contrivance would be much the 
same if the float were dispensed with ; but the float acts advan- 
tageously in hindering the water from rising too high in the 
boiler, should too much feed be admitted, and thereby obviates 
the risk of the water running over into the cylinder. In some 
boilers sheet iron vessels, called sediment collectors, are em- 
ployed, which collect into them the impalpable matter, which 
in Lamb's apparatus is ejected from the boiler at once. One of 
these vessels, of about the size and shape of a loaf of sugar, is 
put into each boiler with the apex of the cone turned down- 
wards into a pipe leading overboard, for conducting the sedi- 
ment away from the boiler. The base of the cone stands some 
distance above the water line, and in its sides conical slits are 
cut, so as to establish a free communication between the water 
within the conical vessel and the water outside it. The parti- 
cles of stony matter which are ballooned to the surface by the 
steam in every other part of the boiler, subside within the cone, 
where, no steam being generated, the water is consequently 



194 CAUSES OF THE CORROSION OF BOILERS. 

tranquil ; and the deposit is discharged overboard by means of 
a i^ipe communicating with the sea. By blowing off from the 
surface of the water, the requisite cleansing action is obtained 
with less waste of heat ; and where the water is muddy, the 
foam upon the surface of the water is ejected from the boiler — 
thereby removing one of the chief causes of priming. 

400. Q. — What is the cause of the rapid corrosion of marine 
boilers ? 

A, — Marine boilers are corroded externally in the region of 
the steam chest by the dripping of water from the deck ; the 
bottom of the boiler is corroded by the action of the bilge 
water, and the ash pits by the practice of quenching the ashes 
with salt water. These sources of injury, however, admit of 
easy remedy ; the top of the boiler may be preserved from ex- 
ternal corrosion by covering it with felt upon which is laid 
sheet lead soldered at every joint so as to be im^Jenetrable to 
water ; the ash pits may be shielded by guard plates which are 
plates fitting into the ash pits and attached to the boiler by a 
few bolts, so that when worn they may be removed and new 
ones substituted, whereby any w^ear upon the boiler in that 
part will be prevented ; and there will be very little wear upon 
the bottom of a boiler if it be imbedded in mastic cement laid 
upon a suitable platform. 

401. Q. — Are not marine boilers subject to internal corro- 
sion ? 

A, — Yes ; the greatest part of the corrosion of a boiler takes 
place in the inside of the steam chest, and the origin of this 
corrosion is one of the obscurest subjects in the whole range of 
engineering. It cannot be from the chemical action of the salt 
water upon the iron, for the flues and other parts of the boiler 
beneath the water suffer very little from corrosion, and in steam 
vessels provided with Hall's condensers, which supply the boiler 
with fresh water, not much increased durability of the boiler 
has been experienced. Nevertheless, marine boilers seldom last 
more than for 5 or 6 years, whereas land boilers made of the 
same quality of iron often last 18 or 20 years, and it does not 
appear probable that land boilers would last a very much 



EXPLANATION OF THE INTERNAL COEROSION. 195 

shorter time if salt water were used in them. The thin film of 
scale spread oyer the parts of a marine boiler situated beneath 
the water, eflfectually protect them from corrosion ; and when 
thQ other parts are completely worn out the fines generally 
remain so perfect, that the hammer marks upon them are as 
conspicuous as at their first formation. The operation of the 
steam in corroding the interior of the boiler is most capricious 
— the parts which are most rapidly worn away in one boiler 
being untouched in another; and in some cases one side of a 
steam chest will be very much wasted away while the opposite 
side remains uninjured. Sometimes the iron exfoliates in the 
shape of a black oxide which comes away in fiakes like the 
leaves of a book, while in other cases the iron appears as if 
eaten away by a strong acid which had a solvent action upon 
it. The application of felt to the outside of a boiler, has in 
several cases been found to accelerate sensibly its internal cor- 
rosion ; boilers in which there is a large accumulation of scale 
appear to be more corroded than where there is no such de- 
posit ; and where the funnel passes through the steam chest the 
iron of the steam chest is invariably much more corroded than 
where the funnel does not pass through it. 

402. Q. — Can you suggest no reason for the rapid internal 
corrosion of marine boilers ? 

A. — The facts which I have enumerated appear to indicate 
that the internal corrosion of marine boilers is attributable 
chiefly to the existence of surcharged steam within them, which 
is steam to which an additional quantity of heat has been com- 
municated subsequently to its generation, so that its tempera- 
ture is greater than is due to its elastic force ; and on this 
hypothesis the observed facts relative to corrosion become to 
some extent explicable. Felt, applied to the outside of a 
boiler, may accelerate its internal corrosion by keeping the 
steam in a surcharged state, when by the dispersion of a part 
of the heat it would cease to be in that state ; boilers in which 
there is a large accumulation of scale must have worked with the 
water very salt, which necessarily produces surcharged steam ; 
for the temperature of steam cannot be less than that of the water 



196 CORROSIVE EFFECT OF SURCHARGED STEAM. 

from which it is generated, and inasmuch as the boiling point 
of water, under any given pressure, rises with the saltness of the 
water, the temperature of the steam must rise with the saltness 
of the water, the pressure remaining the same ; or, in other 
words, the steam must have a higher temperature than is due to 
its elastic force, or be in the state of surcharged steam. The 
circumstance of the chimney flue passing through the steam 
will manifestly surcharge the steam with heat, so that all the 
circumstances which are found to accelerate corrosion, are it 
appears such as would also induce the formation of surcharged 
steam. 

403. Q. — Is it the natural effect of surcharged steam to waste 
away iron ? 

A. — ^It is the natural effect of surcharged steam to oxidate 
the iron with which it is in contact, as is illustrated by the 
familiar process for making hydrogen gas by sending steam 
through a red hot tube filled with pieces of iron ; and although 
the action of the surcharged steam in a boiler is necessarily 
very much weaker than where the iron is red hot, it manifestly 
must have some oxidizing effect, and the amount of corrosion 
produced may be very material where the action is perpetual. 
Boilers with a large extent of heating surface, or with descend- 
ing flues circulating through the cooler water in the bottom of 
the boiler before ascending the chimney, will be less corroded 
internally than boilers in which a large quantity of the heat 
passes away in the smoke ; and the corrosion of the boiler will 
be diminished if the interior of any flue passing through the 
steam be coated vfith fire brick, so as to present the transmis- 
sion of the heat in that situation. The best practice, however, 
appears to consist in the transmission of the smoke through a 
suitable passage on the outside of the boiler, so as to supersede 
the necessity of carrying any flue through the steam at all ; or 
a column of water may be carried round the chimney, into 
which as much of the feed water may be introduced as the heat 
of the chimney is capable of raising to the boiling point, as 
under this limitation the presence of feed water around the 
chimney in the steam chest will fail to condense the steam. 



ARRANGEMENT OF STOP VALVES. 197 

404. Q. — In steam vessels there are usually several boilers ? 
A. — Yes, in steam vessels of considerable power and size. 

405. Q. — ^Are these boilers generally so constructed, that any 
one of them may be thrown out of use ? 

A. — Marine boilers are now generally supplied with stop 
valves, whereby one boiler may be thrown out of use without 
impairing the efficacy of the remainder. These stop valves are 
usually spindle valves of large size, and they are for the most 
part set in a pipe which runs across the steam chests, connecting 
the several boilers together. The spindles of these valves should 
project through stuffing boxes in the covers of the valve chests, 
and they should be balanced by a weighted lever, and kept in 
continual action by the steam. If the valves be lifted up, and 
be suffered to remain up, as is the usual practice, they will be- 
come fixed by corrosion in that position, and it will be impos- 
sible after some time to shut them on an emergency. These 
valves should always be easily accessible from the engine 
room ; and it ought not to be necessary for the coal boxes to 
be empty to gain access to them. 

406. Q. — Should each boiler have at least one safety valve 
for itself? 

A. — Yes ; it would be quite unsafe without this provision, 
as the stop valve might possibly jam. Sometimes valves jam 
from a distortion in the shape of the boiler when a considerable 
pressure is put upon it. 

407. Q. — How is the admission of the water into the boiler 
regulated ? , 

A. — The admission of feed water into the boiler is regulated 
by hand by the engineer by means of cocks, and sometimes by 
spindle valves raised and lowered by a screw. Cocks appear to 
be the preferable expedient, as they are less liable to accident 
or derangement than screw valves, and in modem steam vessels 
they are generally employed. 

408. Q. — At what point of the boiler is the feed intro- 
duced ? 

A. — The feed water is usually conducted from the feed cock 
to a point near the bottom of the boiler by means of an internal 



198 ARRANGEMENT OF FEED APPARATUS. 

pipe, the object of this arrangement being to prevent the rising 
steam from being condensed by the entering water. By being 
introduced near the bottom of the boiler, the water comes into 
contact in the first place with the bottoms of the furnaces and 
flues, and extracts heat from them which could not be extracted 
by water of a higher temperature, whereby a saving of fuel is 
accomplished. In some cases the feed water is introduced into 
a casing around the chimney, from whence it descends into the 
boiler. This plan appears to be an expedient one when the 
boiler is short of heating surface, and more than a usual quan- 
tity of heat ascends the chimney ; but in well proportioned 
boilers a water casing round the chimney is superfluous. When 
a water casing is used the boiler is generally fed by a head of 
water, the feed water being forced up into a small tank, from 
whence it descends into the boiler by the force of gravity, while 
the surplus runs to waste, as in the feeding apparatus of land 
engines. 

409. Q. — Suppose that the engineer should shut ofi" the feed 
water from the boilers while tlie engine was working, what 
would be the result ? 

A, — The result would be to burst the feed pipes, except for 
a safety valve placed on the feed pipe between the engine and 
the boilers, which safety valve opens when any undue pressure 
comes upon the pipes, and allows the water to escape. There 
is, however, generally a cock on the suction side of the feed 
pump, which regulates the quantity of water drawn into the 
pump. But there must be cocks on the boilers also to deter- 
mine into which boiler the water shall be chiefly discharged, 
and these cocks are sometimes all shut accidentally at the same 
time. 

410. Q. — Is there no expedient in use in steam vessels for 
enabling the position of the water level in the boiler to deter- 
mine the quantity of feed water admitted ? 

A. — In some steam vessels floats have been introduced to 
regulate the feed, but their action cannot be depended on in 
agitated water, if applied after the common fashion. Floats 
would probably answer if placed in a cylinder which communi- 



DETAILS OF LOCOMOTIVE BOILERS. 199 

cates with the water in the boiler by means of small holes ; 
and a disc of metal might be attached to the end of a rod ex- 
tending beneath the water level, so as to resist irregular move- 
ments from the motion of the ship at sea, which would other- 
wise impair the action of the apparatus. 

411. Q. — How is the proper level of the water in the boiler 
of a steam vessel maintained when the engine is stopped for 
some time, and the boiler is blowing off steam ? 

A. — By means of a separate pump worked sometimes by 
hand, but usually by a small separate engine called the Donkey 
engine. This pump, by the aid of suitable cocks, will pump 
from the sea into the boiler ; from the sea upon deck either to 
wash decks or to extinguish fiie ; and from the bilge overboard, 
through a suitable orifice in the side of the ship. 



LOCOMOTIVE BOILEES. 

412. Q. — Will you recapitulate the general features of loco- 
motive boilers ? 

A, — Locomotive boilers consist of three portions (see Jig, 
29) : the barrel E, E, containing the tubes, the fire box B, and the 
smoke box F ; of which the barrel smoke box, and external fire 
•box are always of iron, but the internal fire box is generally 
made of copper, though sometimes also it is made of iron. The 
tubes are sometimes of iron, but generally of brass fixed in by 
ferules. The whole of the iron plates of a locomotive boiler 
Which are subjected to the pressure of steam, should be Low- 
Jnoor or Bowling plates of the best quality ; and the copper 
should be coarse grained, rather than rich or soft, and be per- 
fectly free from irregularities of structure and lamination. 

413. Q. — What are the usual dimensions of the barrel ? 

A. — The thickness of the plates composing the barrel of the 
boiler varies generally from -j^ths to ^ths of an inch, and the 
plates should run in the direction of the circumference, so that 
the fibres of the iron may be in the direction of the strain. 
The diameter of the barrel commonly varies from 3 ft. to 3 ft. 6 
inches ; the diameter of the rivets should be from j^ths to ^tha 



200 DETAILS OF THE FIRE BOX. 

of an inch, and the pitch of the rivets or distance betweo clieir 
centres should be from y th to 2 inches. 

414. Q. — How are the fire boxes of a locomotive con- 
structed ? 

A. — The space between the external and internal fire boxes 
forms a water space, which must be stayed every 4^ or 5 inches 
by means of copper or iron stay bolts, screwed through the 
outer fire box into the metal of the inner fire box, and securely 
riveted within it : iron stay bolts are as durable as copper, and 
their superior tenacity gives them an advantage. Sometimes 
tubes are employed as stays. The internal and external fire 
boxes are joined together at the bottom by a N-shaped iron, 
and round the fire door they are connected by means of a cop- 
per ring 1 J in. thick, and 2 in. broad, — the inner fire box being 
dished sufficiently outward at that point, and the outer fire box 
sufficiently inward, to enable a circle of rivets | of an inch in 
diameter passing through the copper ring and the two thick- 
nesses of iron, to make a water-tight joint. The thickness of 
the plates composing the external fire box is in general |ths of 
an inch if the fire box is circular, and from |ths to ^ inch if the 
fire box is square ; and the thickness of the internal fire box is 
in most cases y gths if copper, and from |ths to j^ths of an inch 
if of iron. Circular internal fire boxes, if made of iron, should 
be welded rather than riveted, as the rivet heads are liable to 
be burnt away by the action of the fire ; and when the fire 
boxes are square each side should consist of a single plate, 
turned over at the edges with a radius of 3 inches, for the intro- 
duction of the rivets. 

415. Q. — Is there any provision for stiffening the crown of 
the furnace in a locomotive ? 

A. — The roof of the internal fire box, whether flat as in 
Stephenson's engines, or dome shaped as in Bury's, requires to 
be stiffened with cross stay bars, but the bars require to be 
stronger and more numerous when applied to a flat surface. 
The ends of these stay bars rest above the vertical sides of the 
fire box ; and to the stay bars thus extending across the crown, 
the crown is attached at intervals by means of stay bolts. There 



i 



DETAILS OF THE FIEE BARS. 201 

are projecting bosses upon the stay bars encircling the bolts at 
every point where a bolt goes through, but in the other parts 
they are kept clear of the fire box crown so as to permit the 
access of water to the metal ; and, with the view of facilitating 
the ascent of the steam, the bottom of each stay bar should be 
sharpened away in those parts where it does not touch the 
boiler. 

416. Q. — Is any inconvenience experienced from the intense 
heat in a locomotive furnace ? 

A. — The fire bars in locomotives have always been a source 
of trouble, as from the intensity of the heat in the furnace they 
become so hot as to throw ofi" a scale, and to bend under the 
weight of the fuel. The best alleviation of these evils lies in 
making the bars deep and thin : 4 or 5 inches deep by five 
eighths of an inch thick on the upper side, and three eighths of 
an inch on the under side, are found in practice to be good 
dimensions. In some locomotives a frame carrying a number 
of fire bars is made so that it may be dropped suddenly by 
loosening a catch ; but it is found that any such mechanism 
can rarely be long kept in working order, as the molten clinker 
by running down between the frame and the boiler will gen- 
erally glue the frame into its place. It is therefore found pref- 
erable to fix the frame, and to lift up the bars by the dart used 
by the stoker, when any cause requires the fire to be with- 
drawn. The furnace bars of locomotives are always made of 
malleable iron, and indeed for every species of boiler malleable 
iron bars are to be preferred to bars of cast iron, as they are 
more durable, and may if thin be set closer together, whereby 
the small coal or coke is saved that would otherwise fall into 
the ash pit. The ash box of locomotives is made of plate iron 
a quarter thick : it should not be less than 10 in. deep, and its 
bottom should be about 9 in. above the level of the rails. The 
chimney of a locomotive is made of plate iron one eighth of an 
inch thick : it is usually of the same tliameter as the cylinder, 
but is better smaller, and must not stand more than 14 ft. high 
ibove the level of the rails. 

417. Q. — Are locomotive boilers provided with a steam chest I 



202 MEANS OF ENTSPECTION AND CLEANSING 

A. — The upper portion of the external fire box is usually 
formed into a steam chest, which is sometimes dome shaped, 
sometimes semicircular, and sometimes of a pyramidical form, 
and from this steam chest the steam is conducted away by an 
internal pipe to the cylinders; but in other cases an inde- 
pendent steam chest is set upon the barrel of the boiler, consist- 
ing of a plate iron cylinder, 20 inches in diameter, 2 feet high, 
and three eighths of an inch thick, with a domeshaped top, and 
with the seam welded and the edge turned over to form a flange 
of attachment to the boiler. The pyramidical dome, of the 
form employed in Stephenson's locomotives, presents a consid- 
erable extent of flat surface to the pressure of the steam, and 
this flat surface requires to be very strongly stayed with angle 
irons and tension rods ; whereas the semiglobular dome of the 
kind employed in Bury's engines requires no staying whatever. 
Latterly, however, these domes over the fire box have been 
either much reduced in size or abandoned altogether. 

418. §. — Is any beneficial use made of the surplus steam of 
locomotive ? 

A. — To save the steam which is formed w^hen the engine i 
stationary, a pipe is usually fitted to the boiler, which on a cock 
being turned conducts the steam into the water in the tender, 
whereby the feed water is heated, and less fuel is subsequently 
required. This method of disposing of the surplus steam may 
be adopted when the locomotive is descending inclines, or on 
any occasion where more steam is produced than the engin( 
can consume. 

419. Q. — What means are provided to facilitate the inspe( 
tion and cleaning of locomotive boilers ? 

A, — The man hole, or entrance into the boiler, consists of a 
circular or oval aperture of about 15 in. diameter, placed in 
Bury's locomotive at the apex of the dome, and in Stephenson's 
upon the front of the boiler, a few inches below the level of the 
rounded part ; and the cover of the man hole in Bury's engine 
contains the safety valve seats. In whatever situation this man 
hole is placed, the surfaces of the ring encircling the hole, and 
of the internal part of the door or cover, should be accurately 



I 



TUBES, TUBE PLATES, AND FERULES. 203 

fitted together by scraping or grinding, so that they need only 
the interposition of a little red lead to make them quite tight 
when screwed together. Lead or canvas joints, if of any consid- 
erable thickness, will not long withstand the action of high 
pressure steam ; and the whole of the joints about a locomotive 
should be such that they require nothing more than a little 
paint or putty, or a ring of wi-re gauze smeared with white or 
red lead to make them perfectly tight. There must be a mud 
hole opposite the edge of each water space, if the fire box be 
square, to enable the boiler to be easily cleaned out, and these 
holes are most conveniently closed by screwed plugs made 
slightly taper. A cock for emptying the boiler is usually fixed 
at the bottom of the fire box, and it should be so placed as to 
be accessible when the engine is at work, in order that the 
engine driver may blow off some water if necessary ; but it 
must not be in such a position as to send the water blown off 
among the machinery, as it might carry sand or* grit into the 
bearings, to their manifest injury. 

420. Q. — Will you state the dimensions of the tube plate, 
and the means of securing the tubes in it ? 

A, — The tube plates are generally made from ^ye eighths to 
three fourths of an inch thick, but seven eighths of an inch 
thick appears to be preferable, as when the plate is thick the 
holes will not be so liable to change their figure during the 
process of feruling the tubes : the distance between the tubes 
should never be made less than three fourths of an inch, and 
the holes should be slightly tapered so as to enable the tubes to 
hold the tube plates together. The tubes are secured in the 
tube plates by means of taper ferules driven into the ends of the 
tubes. The ferules are for the most part made of steel at the 
fire box end, and of wrought iron at the smoke box end, though 
ferules of malleable cast iron have in some cases been used with 
advantage: malleable cast iron ferules are almost as easily ex- 
panded when hammered cold upon a mandrel, as the common 
wrought iron ones are at a working heat. Spring steel, rolled 
with a feather edge, to facilitate its conversion into ferules, is 
" supplied by some of the steel-inakers of Shefiield, and it appears 



204 MANDRELS FOR FIXING TUBES. 



• 



^! 



expedient to make use of steel thus prepared when steel ferules 
are employed. In cases where ferules are not employed, it may 
be advisable to set out the tube behind the tube plate by means 
of an expanding mandrel. There are various forms of this in- 
strument. One form is that known as Prosser's expanding 
mandrel, in which there are six or eight segments, which are 
forced out by means of a hexagonal or octagonal wedge, which 
is forced forward by a screw. When the wedge is withdrawn, the 
segments collapse sufficiently to enable them to enter the tube, 
and there is an annular protuberance on the exterior circle of the 
segments, which protuberance, when the mandrel is put into the 
tube, just comes behind the inner edge of the tube plate. When 
the wedge is tightened up by the screw, the protuberance on 
the exterior of the segments composing the mandrel causes a 
corresponding bulge to take place in the tube, at the back oj 
the tube plate, and the tube is thereby brought into more in 
mate contact with the tube plate than would otherwise be the 
case. There is a steel ring indented into the segments of Pros- 
ser's mandrel, to contract the segments when the central wedge 
is withdrawn. A more convenient form of the instrument, how- 
ever, is obtained by placmg the segments in a circular box, 
with one end projecting ; and su23porting each segment in the 
box by a tenon, which fits into a mortise in the cylindrical box. 
To expand the segments, a round tapered piece of steel, like a 
drift, is forced into a central hole, round which the segments 
are arranged. A piece of steel tube, also slit up to enable a 
central drift to expand it, answers very well ; but the thickness 
of that part of the tube in which there requires to be spring 
enough to let the mandrel expand, requires to be sufficiently 
reduced to prevent the pieces from cracking when the central 
drift is driven in by a hammer. The drift is better when mado 
with a globular head, so that it may be struck back by tlv 
hammer, as well as l)e driven in. An expanding mandrel, with 
a central drift, is more rapid in its ojDcration than when the 
expansion is produced by means of a screw. 

421. Q. — Will you explain the means that are adopted to 
regulate the admission of steam to the cylinders ? 



VARIOUS FORMS OF REGULATOR. 205 

A. — In locomotives, the admission of the steam from the 
boiler to the cylinders is regulated by a valve called the regu- 
lator, which is generally placed immediately above the internal 
fire box, and is connected with two copper pipes ; — one con- 
ducting steam from the highest point of the dome down to it, 
and the other conducting the steam that has passed through it 
along the boiler to the upper part of the smoke box. Eegula- 
tors may be divided into two sorts, viz., those with sliding 
valves and steam ports, and those with conical valves and seats, 
of which the latter kind are the best. The former kind have 
for the most part consisted of a circular valve and face, with 
radial apertures, the valve resembling the outstretched wings of 
a butterfly, and being made to revolve on its central pivot by 
connecting links between its outer edges, or by its central spin- 
dle. In some of Stephenson's engines the regulator consists of 
a slide valve covering a port on the top of the valve chests. A 
rod passes from this valve through the smoke box below the 
boiler, and by means of a lever parallel to the starting lever, is 
brought up to the engineer's reach. Cocks were at first used as 
regulators, but were given up, as they were found liable to stick 
fast. A gridiron slide valve has been used by Stephenson, 
which consists of a perforated square moving upon a face with 
an equal number of holes. This plan of a valve gives, with a 
small movement, a large area of opening. In Bury's engines a 
sort of conical plug is used, which is withdrawn by turning the 
handle in front of the fire box : a spiral grove of a very large 
pitch is made in the valve spindle, in which fits a pin fixed to 
the boiler, and by turning the spindle an end motion is given 
to it, which either shuts or opens the steam ]3assage according 
to the direction in which it is turned. The best regulator would 
probably be a valve of the equilibrium description, such as is 
used in the Cornish engine : there would be no friction in such 
a regulator, and it could be opened or shut with a small amount 
of force. Such valves, indeed, are now sometimes employed for 
regulators in locomotives. 
10 



CHAPTER Vm. 

CONSTRUCTIVE DETAILS OF ENGINES. 



rUMPING ENGINES. 



422. Q. — Will you explain the course of procedure in the 
erection of a pumping engine, such as Boulton and Watt intro- 
duced into Cornwall ? 

A, — The best instructions on this subject are those of 
Mr. Watt himself, which are as follows : — Having fixed on the 
proper situation of the pump in the pit, from its centre measure 
out the distance to the centre of the cylinder, from which set 
off all the other dimensions of the house, including the thick- 
ness of the walls, and dig out the whole of the included ground 
to the depth of the bottom of the cellar, so that the bottom of 
the cylinder may stand on a level with the natural ground of 
the place, or lower, if convenient, for the less the height of the 
house above the ground, the firmer it will be. The foundations 
of the walls must be laid at least two feet lower than the bot- 
tom of the cellar, unless the foundation be firm rock ; and care 
must be taken to leave a small drain into the pit quite through 
the lowest part of the foundation of the lever wall, to let off any 
water that may be spilt in the engine house, or may naturally 
come into the cellar. If the foundation at that depth does not 
prove good, you must either go down to a better. if in your 
reach, or make it good by a platform of wood or piles, or both. 



I 



HOUSE FOR PUMPING ENGINE. 20? 

423. Q. — These directions refer to tlie foundations ? 

A. — Yes ; but I will now proceed to the other parts. With- 
in the house, low walls must be built to carry the cylinder 
beams, so as to leave sufficient room to come at the holding 
down bolts, and the ends of these beams must also be lodged in 
the wall. The lever wall must be built in the firmest manner, 
and run solid, course by course, with thin lime mortar, care 
being taken that the lime has not been long slaked. If the 
house be built of stone, let the stones be large and long, and let 
many headers be laid through the wall : it should also be a 
rule, that every stone be laid on the broadest bed it has, and 
never set on its edge. A course or two above the lintel of the 
door that leads to the condenser, build into the wall two par- 
allel flat thin bars of iron equally distant from each other, and 
from the outside and inside of the wall, and reaching the whole 
breadth of the lever wall. About a foot higher in the wall, lay 
at every four feet of the breadth of the front, other bars of the 
same kind at right angles to the former course, and reaching 
quite through the thickness of the wall; and at each front 
comer lay a long bar in the middle of the side walls, and reach- 
ing quite through the front wall ; if these bars are 10 feet or 13 
feet long it will be sufficient. When the house is built up 
nearly to the bottom of the opening under the great beam 
another double course of bars is to be built in, as has been 
directed. At the level of the upper cylinder beams, holes must 
be left in the walls for their ends, with room to move them 
laterally, so that the cylinder may be got in ; and smaller holes 
must be left quite through the walls for the introduction of iron 
bars, which being firmly fastened to the cylinder beams at one 
end, and screwed at the other or outer end, will serve, by their 
going through both the front and back walls, to bind the house 
more firmly together. The spring beams or iron bars fastened 
to them must reach quite through the back wall, and be keyed 
or screwed up tight ; and they must be firmly fastened to the 
lever wall on each side, either by iron bars, firm pieces of wood, 
or long strong stones, reaching far back into the wall. They 



208 HOW TO PACK THE PISTON. 

must also be bedded solidly, and the residue of the opening 
must be built up in tho firmest manner. 

424. Q. — K there be a deficiency of water for the purpose of 
condensation, what course should be pursued ? 

A, — If there be no water in the neighborhood that can be 
employed for the purpose of condensation, it will be necessary 
to make a pond, dug in the earth, for the reception of the water 
delivered by the air pump, to the end that it may be cooled 
and used again for the engine. The pond may be three or four 
feet deep, and lined with turf, puddled, or otherwise made 
water tight. Throwing up the water into the air in the form 
of a jet to cool it, has been found detrimental ; as the water is 
then charged with air which vitiates the vacuum. 

425. ^.— How is the piston of a pumping engine packed ? 
A. — To pack the piston, take sixty common-sized white or 

untarred rope-yarns, and with them plait a gasket or flat rope 
as close and firm as possible, tapering for eighteen inches at 
each end, and long enough to go round the piston, and over- 
lapped for that length ; coil this rope the thin way as hard as 
possible, and beat it with a sledge hammer until its breadth 
answers the place ; put it in and beat it down with a wooden 
drift and a hand mallet, pour some melted tallow all around, 
then pack in a layer of white oakum half an inch thick, so that 
the whole packing may have the depth of ^ye to six inches, 
depending on the size of the engine ; finally, screw down the 
junk ring. The packing should be beat solid, but not too 
hard, otherwise it will create so great a friction as to prevent 
the easy going of the engine. Abimdance of tallow should be 
allowed, especially at first ; the quantity required will be less as 
the cylinder grows smooth. In some of the more modern 
pumping engines, the piston is provided with metallic packing, 
consisting for the most part of a single ring with a tongue piece 
to break the joint, and packed behind with hemp. The upper 
edge of the metallic ring is sharpened away from the inside so 
as to permit more conveniently the application of hemp pack- 
ing behind it ; and the junk ring is made much the same as if 
no metallic i)acking were employed. 



I 



HOW TO START THE ENGINE. 209 

426. Q, — Will you explain the mode of putting the engine 
into operation ? 

A. — To set the engine going, the steam must be raised until 
the pressure in the steam pipe is at least equal to three pounds 
on the square inch ; and when the cylinder jacket is fully 
warmed, and steam issues freely from the jacket cock, open all 
the valves or regulators ; the steam will then forcibly blow out 
the air or water contained in the eduction pipe, and to get rid 
of the air in the cylinder, shut the steam valve after having 
blown through the engine for a few minutes. The cold water 
round the condenser will condense some of the steam contained 
in the eduction pipe, and its place will be supplied by some of 
the air from the cylinder. The steam valve must again be 
opened to blow out that air, and the operation is to be repeated 
until the air is all drawn out of the cylinder. When that is the 
case shut all the valves, and observe if the vacuum gauge shows 
a vacuum in the condenser ; when there is a vacuum equivalent 
to three inches of mercury, open the injection a very little, and 
shut it again immediately ; and if this produces any consider- 
able vacuum, open the exhausting valve a very little way, and 
the injection at the same time. If the engine does not now 
commence its motion, it must be blown through again until it 
moves. If the engine be lightly loaded, or if there be no water 
in the pumps, the throttle valve must be kept nearly closed, and 
the top and exhaustion regulators must be opened only a very 
little way, else the engine will make its stroke with violence, and 
perhaps do mischief. If there is much unbalanced weight on 
the pump end, the plug which opens the steam valve must be 
so regulated, that the valve will only be opened very slightly ; 
and if after a few strokes it is found that the engine goes out 
too slowly, the valve may be then so adjusted as to open wider. 
The engine should always be made to work full stroke, that is, 
until the catch pins be made to come within half an inch of the 
springs at each end, and the piston should stand high enough 
in the cylinder when the engine is at rest, to spill over into the 
perpendicular steam pipe any water which may be condensed 
above it ; for if water remain upon the piston, it will increase 



210 OPERATION OF BLOWING THROUGH. 

tlie consumption of steam. When the engine is to be stopped, 
shut the injection valve and secure it, and adjust the tappets so 
as to jDrevent the exhausting valve from opening and to allow 
the steam valve to open and remain open, otherwise, a partial 
vacuum may arise in the cylinder, and it may be filled with 
water from the injection or from leaks. A single acting engine, 
when it is in good order, ought to be capable of going as slow 
as one stroke in ten minutes, and as fast as ten strokes in one 
minute ; and if it does not fulfil these conditions, there is some 
fault which should be ascertained and remedied. 

427. Q. — Your explanation has reference to the pumping 
engine as introduced into Cornwall by Watt : have any modi- 
fications been since made upon it ? 

A. — In the modem Cornish engines the steam is used very 
expansively, and a high pressure of steam is employed. In 
some cases a double cylinder engine is used, in which the steam, 
after having given motion to a small piston on the principle of 
a high pressure engine, passes into a larger cylinder, where it 
operates on the principle of a condensing engine ; but there is 
no superior efiect gained by the use of two cylinders, and there 
is greater complexity in the apparatus. Instead of the lever 
walls, cast iron columns are now frequently used for supporting 
the main beam in pumping engines, and the cylinder end of the 
main beam is generally made longer than the pump end in 
engines made in Cornwall, so as to enable the cylinder to have 
a long stroke, and the piston to move quickly, without com- 
municating such a velocity to the pump buckets as will make 
them work with such a shock as to wear themselves out quick- 
ly. A high pressure of steam, too, can be employed where the 
stroke is long, without involving the necessity of making the 
working parts of such large dimensions as would otherwise be 
necessary ; for the strength of the parts of a single acting engine 
will require to be much the same, whatever the length of the 
stroke may be. 

428. Q. — What kind of pump is mostly used in draining 
deep mines ? 

A, — The pump now universally preferred is the plunger 



HARVEY AND WESt's PUMP YALVES 211 

pump, wliicli admits of being packed or tightened while tlie 
engine is at work ; but the lowest lift of a mine is generally 
supplied with a pump on the suction principle, both with the 
view of enabling the lowest pipe to follow the w^ater wdth 
facility as the shaft is sunk deeper, and to obviate the incon- 
venience of the valves of the pump being rendered inaccessible 
by any flooding in the mine. The pump valves of deep mines 
are a perpetual source of expense and trouble, as from the press- 
ure of water upon them it is difficult to prevent them from clos- 
ing with violence ; and many expedients have been contrived 
to mitigate the evil, of which the valve known as Harvey and 
West's valve has perhaps gained the widest acceptation. 

429. Q. — Will you describe Harvey and West's pump valve ? 

A, — This valve is a compromise between the equilibrium 
valve, of the kind employed for admitting the steam to. and 
from the cylinder in single acting engines, and the common 
spindle valve formerly used for that purpose ; and to compre- 
hend its action, it is necessary that the action of the equilibrium 
valve, which has been already represented in^^. 34, should first 
be understood. This valve consists substantially of a cylinder 
open at both ends, and capable of sliding upon a stationary pis- 
ton fixed upon a rod the length of the cylinder, which proceeds 
from the centre of the orifice the valve is intended to close. It 
is clear, that when the cylinder is pressed down until its edge 
rests upon the bottom of the box containing it, the orifice of 
the pipe must be closed, as the steam can r.Gither escape past 
the edge of the cylinder nor between the cylinder and the pis- 
ton ; and it is equally clear, that as the pressure upon the cylin- 
der is equal all around it, and the whole of the downward 
pressure is maintained by the stationary piston, the cylinder 
can be raised or lowered without any further exertion of force 
than is necessary to overcome the friction of the piston and of 
the rod by which the cylinder is raised. Instead of the rubbing 
surface of a piston, how^ever, a conical valve face between the 
cylinder and piston is employed, which is tight only when the 
cylinder is in its lowest position ; and there is a similar face 
between the edge of the cylinder and the bottom of the box in 



212 STRIKE ON A COMPOSITJION OF LEAD AND TIN. 






wliich it is placed. The moving part of tlie valve, too, instead 
of being a perfect cylinder, is bulged outward in the middle, so 
as to permit the steam to escape j)ast the stationary piston when 
the cylindrical part of the valve is raised. It is clear, that if 
such a valve were applied to a pump, no pressure of water 
within the jDump would suffice to open it, neither would any 
pressure of water above the valve cause it to shut with violence ; 
and if an equilibrium valve, therefore, be used as a pump valve 
at all, it must be opened and shut by mechanical means. In 
Harvey and West's valves, however, the equilibrium principle 
is only partially adopted ; the lower face is considerably larger 
in diameter than the upper face, and the dijfference constitutes 
an annulus of pressure, which will cause the valve to open or 
shut with the same force as a spindle valve of the area of the 
annulus. To deaden the shock still more effectually, the lower 
face of the valve is made to strike upon end wood driven into 
an annular recess in the pump bucket ; and valves thus con- 
structed work with very little noise or tremor ; but it is found 
in practice, that the use of Harvey and West's valve, or any 
contrivance of a similar kind, adds materially to the load upon 
the pump, especially in low lifts where the addition of a loaxl 
to the valve makes a material addition to the total resistance 
which the engine has to overcome. Instead of end wood driven 
into a recess for the valve to strike upon, a mixture of tin and 
lead cast in a recess is now frequently used, and is found to be 
preferable to the wood. 

430. Q. — Is there any other kind of pump valve w^hich is free 
from the shocks incidental to the working of common valves ? 

A. — In some cases canvass valves are used for pumps, with 
the effect of materially mitigating the shock ; but they require 
frequent renewal, and are of inferior eligibility in their action 
to the slide valve, which might in many cases be applied to 
pumps without inconvenience. 

431. Q. — Could not a form of pump be devised capable of 
working without valves at all ? 

A. — It appears probable, that by working a common recipro- 
cating pump at a high speed, a continuous flow of water might 



IMPENDING SUPERSESSION OP CORNISH ENGINES. 213 

be maintained througli the pipes in such a way as to render the 
existence of any valves superfluous after once the action was 
begun, the momentum of the moving water acting in fact as 
valves. The centrifugal pump, however, threatens to supersede 
pumps of every other kind ; and if the centrifugal pump be 
employed there will be no necessity for pump valves at all. 
There is less loss of effect by the centrifugal pump than by the 
common pump. 

432. Q. — What is the best form of the centrifugal pump ? 
-4.— There are two forms in which the centrifugal pump 

may be applied to mines ; — that in which the arms diverge from 
the bottom, like the letter Y ; and that in which revolving arms 
are set in a tight case near the bottom of the mine, and are 
turned by a shaft from the surface. Such pumps both draw 
and force ; and either by arranging them in a succession of lifts 
in the shaft of the mine, or otherwise, the water may be drawn 
without inconvenience from any depth. The introduction of 
the centrifugal pump would obviously extinguish the single 
acting engine, as rotative engines working at a high speed 
would be the most appropriate form of engine where the cen- 
trifugal pump was employed. 

433. Q. — This would not be a heavy deprivation ? 

A, — The single acting engine is a remnant of engineering 
barbarism which must now be superseded by more compendious 
contrivances. The Cornish engines, though rudely manufac- 
tured, are very expensive in production, as a large engine does 
but little work ; whereas by employing a smaller engine, mov- 
ing with a high speed, the dimensions may be so far diminished 
that' the most refined machinery may be obtained at less than 
the present cost. 

434. Q, — Are not the Cornish engines more economical in 
fuel than other engines ? 

A. — It is a mistake to suppose that there is any peculiar vir- 
tue in the existing form of Cornish engine to make it econom- 
ical in fuel, or that a less lethargic engine would necessarily be 
less efficient. The large duty of the engines in Cornwall is 
traceable to the large employment of the principle of expansion, 



214 MERITS OF OSCILLATING ENGINES, 

and to a few other causes wliicli may be made of quite as deci- 
sive efficacy in smaller engines working with a quicker speed ; 
and there is therefore no argument in the performance of the 
present engines against the proposed substitution. 

VAKIOUS FORMS OF MAEINE ENGINES. 

435. Q. — What species of paddle engine do you consider to 
be the best ? 

A. — The oscillating engine. 

436. Q. — Will you explain the grounds of that preference ? 
A, — The engine occupies little space, consists of few parts, is 

easily accessible for repairs, and may be both light and strong 
at the same time. In the case of large engines the crank in the 
intermediate shaft is a disadvantage, as it is difficult to obtain 
such a forging quite sound. But by forging it in three cranked 
flat bars, which are then laid together and welded into a square 
shaft, a sound forging will be more probable, and the bars 
should be rounded a little on the sides which are welded to 
allow the scoriae to escape during that operation. It is impor- 
tant in so large a forging not to let the fire be too fierce, else 
the surface of the iron will be burnt before the heart is brought 
to a welding heat. In some cases in oscillatiog engines the air 
pump has been wrought by an eccentric, and that may at any 
time be done where doubt of obtaining a sound intermediate 
shaft is entertained ; but the precaution must be taken to make 
the eccentric very wide so as to distribute the pressure over a 
large surface, else the eccentric will be apt to heat. 

437. Q. — Have not objections been brought against the oscil- 
lating engine ? 

A. — In common with every other improvement, the oscillat- 
ing engine, at the time of its introduction, encountered much 
oj)position. The cylinder, it was said, would become oval, tbe 
trunnion bearings would be liable to heat and the trunnion 
joints to leak, the strain uj)on the trunnions would be apt to 
bend in or bend out the sides of the cylinder ; and the circum- 
stance of the cylinder being fixed across its centre, while the 



MANAGEMENT OF TRUNNION PACKINGS. 215 

sliaft requires to accommodate itself to the working of the ship, 
might, it was thought, be the occasion of such a strain upon 
the trunnions as would either break them or bend the piston 
rod. It is a sufficient reply to these objections to say that they 
are all hypothetical, and that none of them in practice have 
been found to exist — to such an extent at least as to occasion 
any inconvenience ; but it is not difficult to show that they are 
altogether unsubstantial, even without a recourse to the dis- 
proofs afforded by experience. 

438. Q. — Is there not a liability in the cylinder to become 
oval from the strain thrown on it by the piston ? 

A, — There is, no doubt, a tendency in oscillating engines for 
the cylinder and the stuffing box to become oval, but after a 
number of years' wear it is found that the amount of ellipticity 
is less than that which is found to exist in the cylinders of side 
lever engines after a similar trial. The resistance opposed by 
friction to the oscillation of the cylinder is so small, that a mar^ 
is capable of moving a large cylinder with one hand ; whereas 
in the side lever engine, if the parallel motion be in the least 
untrue, which is, at sonie time or other, an almost inevitable 
condition, the piston is pushed with great force against the 
side of the cylinder, whereby a large amount of wear and fric- 
tion is occasioned. The trunnion bearings, instead of being 
liable to heat like other journals, are kept down to the tempera- 
ture of the steam by the flow of steam passing through them ; 
and the trunnion packings are not liable to leak when the pack- 
ings, before being introduced, are squeezed in a cylindrical 
mould. 

439. Q. — Might not the eduction trunnions be immersed in 
water ? 

A. — In some cases a hollow, or lantern brass, about one third 
or one fourth the length of the packing space, and supplied 
with steam or water by a pipe, is introduced in the middle of 
the packing, so that if there be any leakage through the trun- 
nion, it will be a leakage of steam or water, which will not 
vitiate the vacuum ; but in ordinary cases this device will not 
be necessary, and it is not commonly employed. It is clear that 



216 INFERIOR . ELIGIBILITY OF TRUNK ENGINES. 

there can be no buckling of the sides of the cylinder by the 
strain upon the trunnions, if the cylinder be made strong 
enough, and in cylinders of the ordinary thickness such an 
action has never been experienced ; nor is it the fact, that the 
intermediate shaft of steam vessels, to which part alone the 
motion is communicated by the engine, requires to adapt itself 
to the altering forms of the vessel, as the engine and interme- 
diate shaft are rigidly connected, although the paddle shaft 
requires to be capable of such an adaptation. Even if this 
objection existed, however, it could easily be met by making 
the crank pin of the ball and socket fashion, which would per- 
mit the position of the intermediate shaft, relatively with that 
of the cylinder, to be slightly changed, without throwing an 
imdue strain upon any of the working parts. 

440. Q, — Is the trunk engine inferior to the oscillating ? 

A. — A very elegant and efficient arrangement of trunk en- 
gine suitable for paddle vessels has latterly been employed by 
Messrs. Ilennie, of which all the parts resemble those of Penn's 
oscillating engine except that the cylinders are stationary in- 
stead of being movable ; and a round trunk or pipe set u^Don 
the piston, and moving steam tight through the cylinder cover, 
enables the connecting rod which is fixed to the piston to 
vibrate within it to the requisite extent. But the vice of all 
trunk engines is that they are necessarily more wasteful of 
steam, as the large mass of metal entering into the composition 
of the trunk, moving as it does alternately into the atmosphere 
and the steam, must cool and condense a part of the steam. 
The radiation of heat from the interior of the trunk will have 
the same operation, though in vertical trunk engines the loss 
from this cause might probably be reduced by filling the trunk 
with oil, so far as this could be done without the oil being M 
spilt over the edge. 1 

441. Q. — What species of screw engine do you consider the 
best ? 

A. — I am inclined to give the preference to a variety of the 
horizontal steeple engine, such as w^as first used in H. M. S. 
Amphion. In this engine the cylinders lie on their sides, and 



BEST FORM OF ENGINE FOR THE SCREW. 217 

they are placed near the side of the vessel with their mouths 
pointing to the keel. From each cylinder two long piston rods 
proceed across the vessel to a cross head working in guides ; 
and from this cross head a connecting rod returns back to the 
centre of the vessel and gives motion to the crank. The piston 
rods are so placed in the piston that one of them passes above 
the crank shaft, and the other below the crank shaft. The 
cross head lies in the same horizontal plane as the centre of tlio 
cylinder, and a lug projects upwards from the cross head to 
engage one piston rod, and downwards from the cross head to 
engage the other piston rod. The air pump is double acting, 
and its piston or bucket has the same stroke as the piston of the 
engine. The air pump bucket derives its motion from an arm 
on the cross head, and a similar arm is usually employed in 
engines of this class to work the feed and bilge pumps. 

442. Q. — Is not inconvenience experienced in direct acting 
screw engines from the great velocity of their motion ? 

A, — Not if they are properly constructed ; but they require 
to be much stronger, to be fitted with more care, and to have 
the bearing surfaces much larger than is necessary in engines 
moving slowly. The momentum of the reciprocating parts 
should also be balanced by a weight applied to the crank or 
crank shaft, as is done in locomotives. A very convenient 
arrangement for obtaining surface is to form the crank of each 
engine of two cast iron discs cast with heavy sides, the excess 
of weight upon the heavy sides being nearly equal to that of 
the piston and its connections. When the piston is travelling 
in one direction the weights are travelling in the opposite ; and 
the momentum of the piston and its attachments, which is ar- 
rested at each reciprocation, is just balanced by the equal and 
opposite momentum of the weights. One advantage of the 
horizontal engine is, that a single engine may be employed, 
whereby greater simplicity of the machinery and greater 
economy of fuel will be obtained, since there will be less 
radiating surface in one cylinder than in two. 



218 ADVANTAGES OF STEAM JACKETS. 

CYLINDERS, PISTONS, AND VALVES, 

443. Q. — Is it a beneficial practice to make cylinders with 
steam jackets ? 

^.— In Cornwall, where great attention is paid to economy 
of fuel, all tlie engines are made with steam jackets, and in 
some cases a flue winds spirally round the cylinder, for keeping 
the steam hot. Mr. Watt, in his early practice, discarded the 
steam jacket for a time, but resumed it again, as he found its 
discontinuance occasioned a perceptible waste of fuel ; and in 
modem engines it has been found that where a jacket is used 
less coal is consumed than where the use of a jacket is rejected. 
The cause of this diminished effect is not of very easy percep- 
tion, for the jacket exposes a larger radiating surface for the 
escape of the heat than the cylinder ; nevertheless, the fact has 
been established beyond doubt by repeated trials, that engines 
provided with a jacket are more economical than engines with- 
out one. The exterior of the cylinder, or jacket, should be 
covered with several plies of felt, and then be cased in timber, 
which must be very narrow, the boards being first dried in a 
stove, and then bound round the cylinder with hoops, like the 
staves of a cask. In many of the Cornish engines the steam is 
let into casings formed in the cylinder cover and cylinder 
bottom, for the further economisation of the heat, and the cylm- 
der stuffing box is made very deep, and a lantern or hollow 
brass is introduced into the centre of the packing, into which 
brass the steam gains admission by a pipe provided for the 
purjDose ; so that in the event of the packing becoming leaky, 
it will be steam that will be leaked into the cylinder instead 
of air, which, being incondensable, would impair the efficiency 
of the engine. A lantern brass, of a similar kind, is sometimes 
introduced into the stuffing boxes of oscillating engines, but 
its use there is to receive the lateral pressure of the piston rod, 
and thus take any strain off the packing. 

444. Q. — Will you explain the ]3roper course to pursue in 
the production of cylinders ? 

A, — In all engines the valve casing, if made in a separate 



CONSTRUCTION OF CYLINDERS AND STUFFING BOXES. 219 

piece from the cylinder, should be attached by means of a 
metallic joint, as such a barbarism as a rust joint in such situa- 
tions is no longer permissible. In the case of large engines 
with valve casings suitable for long slides, an expansion joint in 
the valve casing should invariably be inserted, otherwise the 
steam, by gaining admission to the valve casing before it can 
enter the cylinder, expands the casing while the cylinder re- 
mains unaltered in its dimensions, and the joints are damaged, 
and in some cases the cylinder is cracked by the great strain 
thus introduced. The chest of the blow-through valve is very 
commonly cast upon the valve casing ; and in engines where 
the cylinders are stationary this is the most convenient prac- 
tice. All engines, where the valve is not of such a construction 
as to leave the face when a pressure exceeding that of the steam 
is created in the cylinder by priming or otherwise, should be 
provided with an escape valve to let out the water, and such 
valve should be so constructed that the water cannot fly out 
with violence over the attendants ; but it should be conducted 
away by a suitable pipe, to a place where its discharge can 
occasion no inconvenience. The stuffing boxes of all engines 
which cannot be stopped frequently to be repacked, should be 
made very deep ; metallic packing in the stuffing box has been 
used in some engines, consisting in most instances of one or 
more rings, cut, sprung, and slipped upon the piston rod before 
the cross head is put on, and packed with hemp behind. This 
species of packing answers very well when the parallel motion 
is true, and the piston rod free from scratches, and it accom- 
plishes a material saving of tallow. In some cases a piece of 
sheet brass, packed behind with hemp, has been introduced 
with good effect, a flange being turned over on the under edge 
of the brass to prevent it from slipping up or down "vvdth the 
motion of the rod. The sheet brass speedily puts an excellent 
polish upon the rod, and such a packing is more easily kept, 
and requires less tallow than where hemp alone is employed. 
In side lever marine engines the attachments of the cylinder to 
the diagonal stay are generally made of too small an area, and 
the flanges are made too thick. A very thick flange cast on 



220 BEST VARIETIES OF PISTON. 

any part of a cylinder endangers the soundness of the cylinder, 
by inducing an unequal contraction of the metal ; and it is a 
preferable course to make the flange for the attachment or the 
framing thin, and the surface large — the bolts being turned 
bolts and nicely fitted. If from malformation in this part the 
framing works to an inconvenient extent, the best expedient 
appears to be the introduction of a number of steel tapered 
bolts, the holes having been previously bored out ; and if the 
flanges be thick enough, square keys may also be introducer!, 
half into one flange and half into the other, so as to receive the 
strain. If the jaw cracks or breaks away, however, it will be 
best to apply a malleable iron hoop around the cylinder to take 
the strain, and this will in all cases be the preferable expedient, 
where from any peculiarities of structure there is a difficulty in 
introducing bolts and keys of sufficient strength. 

445. Q. — Which is the most eligible species of piston ? 

A, — For large engines, pistons with a metallic packing, con-, 
sisting of a single ring, with the ends morticed into one another, 
and a piece of metal let in flush over the joint and riveted to 
one end of the ring, appears to be the best species of piston ; 
and if the cylinder be oscillating, it will be expedient to cham- 
fer off the upper edge of the ring on the inner side, and to pack 
it at the back with hemp. If the cylinder be a stationary one, 
springs may be substituted for the hemp packing, but in any 
case it will be expedient to make the vertical joints of the ends 
of the ring run a little obliquely, so as to prevent the joint form- 
ing a ridge in the cylinder. For small pistons two rings may 
be employed, made somewhat eccentric internally to give a 
greater thickness of metal in the centre of the ring ; these rings 
must be set one above the other in the cylinder, and the joints, 
which are oblique, must be set at right angles with one another, 
so as to obviate any disposition of the rings, in their expansion, 
to wear the cylinder oval. The rings must first be turned a 
little larger than the diameter of the cylinder, and a piece is 
then to be cut out, so that when the ends are brought together 
the ring wUl just enter within the cylinder. The ring, while 
retained in a state of compression, is then to be put in the lathe 



MODE OF FITTING PISTON EINGS. 221 

and turned very truly, and finally it is to be hammered on the 
inside with the small end of the hammer, to expand the metal, 
and thus increase the elasticity. 

446. Q. — The rings should be carefully fitted to one another 
laterally ? 

A, — The rings are to be fitted laterally to the piston, and to 
one another, by scraping — a steady pin being fixed upon the 
flange of the piston, and fitting into a corresponding hole in 
the lower ring, to keep the lower ring from turning round ; and 
a similar pin being fixed into the top edge of the lower ring to 
prevent the upper ring from turning round ; but the holes into 
which these pins fit must be made oblong, to enable the rings 
to press outward as the rubbing surfaces wear. In most cases 
it will be expedient to press the packing rings out with springs 
where they are not packed behind with hemp, and the springs 
should be made very strong, as the prevailing fault of springs is 
their weakness. Sometimes short bent springs, set round at 
regular intervals between the packing rings and body of the 
piston, are employed, the centre of each spring being secured 
by a steady pin or bolt screwed into the side of the piston ; but 
it will not signify much what kind of springs is used, provided 
they have sufficient tension. When pistons are made of a single 
ring, or of a succession of single rings, the strength of each ring 
should be tested previously to its introduction into the piston, 
by means of a lever loaded by a heavy weight. 

447. §. — What kind of piston is employed by Messrs. Penn ? 
A, — Messrs. Penn's piston for oscillating engines has a single 

packing ring, with a tongue piece, or mortice end, made in the 
manner already described. The ring is packed behind with 
hemp packing, and the piece of metal which covers the joint is 
a piece of thick sheet copper or brass, and is indented into the 
iron of the ring, so as to ofier no obstruction to the application 
of the hemp. The ring is fitted to the piston only on the under 
edge ; the top edge is rounded to a point from the inside, and 
the junk ring does not bear upon it, but the junk ring squeezes 
down the hemp packing between the packing ring and th# 
body of the piston. 



222 ATTACHMENT OF PISTON EOD TO PISTON. 

448. Q. — How should the piston rod be secured to the 
piston ? 

A, — The piston rod, where it fits into the piston, should 
have a good deal of taper ; for if the taper be too small the rod 
will be drawn through the hole, and the piston will be split 
asunder. Small grooves are sometimes turned out of the piston 
rod above and below the cutter hole, and hemp is introduced 
in order to make the piston eye tight. Most piston rods are 
fixed to the piston by means of a gib and cutter, but in some 
cases the upper portion of the rod within the eye is screwed, 
and it is fixed into the piston by means of an indented nut. 
This nut is in some cases hexagonal, and in other cases the ex- 
terior forms a portion of a cone which completely fills a corre- 
sponding recess in the piston ; but nuts made in this way 
become rusted into their seat after some time, and cannot be 
started again without much difficulty. Messrs. Miller, Raven- 
hill & Co. fix in their piston rods by means of an indented 
hexagonal nut, which may be started by means of an open box 
key. The thread of the screw is made flat upon the one side 
and much slanted on the other, whereby a greater strength is 
secured, without creating any disposition to spilt the nut. In 
side lever engines it is a judicious practice to add a nut to the 
top of the piston rod, in addition to the cutter for securing the 
piston rod to the cross head. In a good example of an engine 
thus provided, the piston rod is 7 in. in diameter, and the screw 
5 in. ; the part of the rod which fits into the cross head eye is 1 
ft. 5h in. long, and tapers from 6^ in. to 6}-^ in. diameter. This 
proportion of taper is a good one ; if the taper be less, or if a 
portion of the piston rod within the cross head eye be left un- 
tai^ered, as is sometimes the case, it is very difllcult to detach 
the parts from one another. 

449. Q. — Which is the most beneficial construction of slide 
valve ? 

A. — The best construction of slide valve appears to be that 
adopted by Messrs. Pcnn for their larger engines, and which con- 
sists of a three ported valve, to the back of which a ring is ap- 
plied of an area equal to that of exhaustion port, and which, by 



BEST FORMS OP SLIDE VALVES. 223 

bearing steam tight against the back of the casing, so that a 
vacuum may be maintained within the ring, puts the valve in 
equilibrium, so that it may be moved with an inconsiderable 
exercise of force. The back of the valve casing is put on like a 
door, and its internal surface is made very true by scraping. 
There is a hole through the valve so as to conduct away any 
steam which may enter within the ring by leakage, and the 
ring is kept tight against the back of the casing by means of a 
ring situated beneath the bearing ring, provided with four lugs, 
through which bolts pass tapped into bosses oh the back of the 
valve ; and, by unscrewing these bolts, — which may be done by 
means of a box key which passes through holes in the casing 
closed with screwed plugs, — the lower ring is raised upwards, 
carrying the bearing ring before it. The rings must obviously 
be fitted over a boss upon the back of the valve ; and between 
the rings, which are of brass, a gasket ring is interposed to 
compensate by its compressibility for any irregularity of pres- 
sure, and each of the bolts is provided with a ratchet collar to 
prevent it from turning back, so that the engineer, in tighten- 
ing these bolts, will have no difficulty in tightening them 
equally, if he counts the number of clicks made by the ratchet. 
Where this species of valve is used, it is indispensable that 
large escape valves be applied to the cylinder, as a valve on 
this construction is unable to leave the face. In locomotive 
engines, the valve universally employed is the common three 
ported valve. 

450. Q. — Might not an equilibrium valve be so constructed 
by the interposition of springs, as to enable it to leave the 
cylinder face when an internal force is applied ? 

A. — That can no doubt be done, and in some engines has 
been done. In the screw steamer Azof, the valve is of the 
equilibrium construction, but the plate which carries the pack- 
ing on which the top ring rests, is an octagon, and fits into an 
octagonal recess on the back of the valve. Below each side of 
the octagon there is a bent flat spring, which lifts up the octag- 
onal plate, and with it the packing ring agamst the back of 
the valve casing; and should water get into the cylinder, it 



224 



EQUILIBRIUM GEIDIRON SLIDE VALVES. 



escapes by lifting the valve, wliich is rendered possible by the 
com]3ressibility of the springs. An equivalent arrangement is 
shown in figs. 39 and 40, where the ring is lifted by spiral 
springs. 

Fig. 39. 




Equilibrium Gridiron Slide Valve. 
Longitudinal Section. Scale f inch = 1 foot. 

451. Q, — What species of valve is that shown in. figs. 39 
and 40 ? 

A, — It is an equilibrium gridiron valve ; so called because 
it lets the steam in and out by more than one port, a a are 

Fig. 40. 




Equilibrium Gridiron Slide Valve. 
Back View with Iling removed. Scale f inch = 1 foot. 

the ordinary steam passages to the top and bottom of the 
cylinder ; b b is the ring which rubs against the back of the 



CONSTRUCTION OF THE ECCENTRIC. 225 

valve casing, and d is tlie eduction passage, s s s s sliows the 
limits of the steam space, for thg steam penetrates to the cen- 
tral chamber s s by the sides of the valve. When the valve is 
opened upon the steam side, the cylinder receives steam through 
both ports at that end of the cylinder, and both ports at the 
other end of the cylinder are at the same time open to the 
eduction. The benefit of this species of valve is, that it gives 
the same opening of the valve that is given in ordinary engines, 
with half the amount of travel ; or if three ports were made 
instead of two, then it would give the same area of opening 
that is given in common engines with one third the amount of 
travel. For direct acting screw engines this species of valve is 
now extensively used. 

452. Q. — Will you describe the configuration and mode of 
attachment of the eccentric by which the valve is moved ? 

A.—Jji marine engines, whether paddle or screw, if moving 
at a slow rate of speed, the eccentric is generally loose upon the 
shaft, for the purpose of backing, and is furnished with a back 
balance and catches, so that it may stand either in the position 
for going ahead, or in that for going astern. The body of the 
eccentric is of cast iron, and it is put on the shaft in two pieces. 
The halves are put together with rebated joints to keep them 
from separating laterally, and they are prevented from sliding 
out by round steel pins, each ground into both halves ; square 
keys would probably be preferable to round pins in this ar- 
rangement, as the pins tend to wedge the jaws of the eccentric 
asunder. In some cases the halves of the eccentric are bolted 
together by means of flanges, which is, perhaps, the preferable 
practice. The eccentric hoop in marine and land engines is 
generally of brass ; it is expedient to cast an oil cup on the 
eccentric hoop, and, where practicable, a pan should be placed 
beneath the eccentric for the reception of the oil droppings. 
The notch of the eccentric rod for the reception of the pin of 
the valve shaft is usually steeled, to prevent inconvenient wear ; 
for when the sides of the notch wear, the valve movement is 
not only disturbed, but it is very difficult to throw the eccentric 
rod out of gear. It is found to be preferable, however, to fit 



226 DETAILS OF THE AIR PUMP. 

this notcli witli a brass bush, for the wear is then less rapid, 
and it is an easy thing to replace this bush with another when 
it becomes worn. The eccentric catches of the kind usually 
employed in marine engines, sometimes break off at the first 
bolt hole, and it is preferable to have a bolt in advance of the 
catch face, or to have a hoop encircling the shaft with the 
catches welded on it, the hoop itself being fixed by bolts or a 
key. This hoop may either be put on before the cranks in one 
piece or afterwards in two pieces. 

453. Q. — Are such eccentrics used in direct acting screw 
engines ? 

^.— No ; direct acting screw engines are usually fitted with 
the link motion and two fixed eccentrics. 



AIR PUMP AND CONDENSER. 

454. Q. — What are the details of the air pump ? 

A. — The air pump bucket and valves are all of brass in 
modern marine engines, and the chamber of the pump is lined 
with copper, or made wholly of^ brass, whereby a single boring 
suffices. When a copper lining is used, the pump is first bored 
out, and a bent sheet of copper is introduced, which is made 
accurately to fill the place, by hammering the copper on the 
inside. Air pump rods of Muntz's metal or copper are much 
used. Iron rods covered with brass are generally wasted away 
where the bottom cone fits into the bucket eye, and if the cas- 
ing be at all porous, the water will insinuate itself between the 
casing and the rod and eat away the iron. If iron rods covered 
with brass be used, the brass casing should come some distance 
into the bucket eye ; the cutter should be of brass, and a brass 
washer should cover the under side of the eye, so as to defend 
the end of the rod from the salt water. Rods of Muntz's metal 
are probably on the whole to be preferred. It is a good prac- 
tice to put a nut on the top of the rod, to secure it more firmly 
in the cross head eye, where that plan can be conveniently 
adopted. The part of the rod which fits into the cross head 
eye should have more taper when made of coj^per or brass, than 



VARIOUS FORMS OF DELIVERY VALVE. 227 

when made of iron ; as, if the taper be small, the rod may 
get staved into the eye, whereby its detachment will be 
difficult. 

455. Q. — What species of packing is used in air pumps ? 

A. — Metallic packing has in some instances been employed 
in air pump buckets, but its success has not been such as to 
lead to its further adoption. The packing commonly employed 
is hemp. A deep solid block of metal, however, without any 
packing, is often employed with a satisfactory result ; but this 
block should have circular grooves cut round its edge to hold 
water. Where ordinary packing is employed, the bucket should 
always be made with a junk ring, whereby the packing may be 
easily screwed down at any time with facility. In slow moving 
engines the bucket valve is generally of the spindle or pot-lid 
kind, but butterfly valves are sometimes used. The foot and 
delivery valves are for the most part of the flap or hanging 
kind. These valves all make a considerable noise in working, 
and are objectionable in many ways. Valves on Belidor's con- 
struction, which is in efiect that of a throttle valve hung off the 
centre, were some years ago proposed for the delivery and foot 
valves ; and it appears probable that their operation would be 
more satisfactory than that of the valves usually employed. 

456. Q. — Where is the delivery valve usually situated ? 
J..— Some delivery valve seats are bolted into the mouth of 

the air pump, whereby access to the pump bucket is rendered 
difficult : but more commonly the delivery valve is a flap valve 
exterior to the pump. If delivery valve seats be put in the 
mouth of the air pump at all, the best mode of fixing them ap- 
pears to be that adopted by Messrs. Maudslay. The top of the 
pump barrel is made quite fair across, and upon this flat sur- 
face a plate containing the delivery valve is set, there being a 
small ledge all round- to keep it steady. Between the bottom 
of the staffing box of the pump cover and the eye of the valve 
seat a short pipe extends encircling the pump rod, its lower 
end checked into the eye of the valve seat, and its upper end 
widening out to form the bottom of the stuffing box of the 
pump cover. Upon the top of this pipe some screws press, 



228 



TRUNK AIR PUMPS. 



whicli are accessible from the top of the stuffing box gland, and 
the packing also aids in keeping down the pipe, the function 
of which is to retain the valve seat in its place. When the 

pump bucket has to be ex- 

^^•^^ * amined the valve seat may 

/ "'' be slung with the cover, so 

/ as to come up with the same 

/''-fr:, purchase. For the bucket 

*:1 i' valves of such pumps Messrs. 

; \ \ ^^.. Maudslay employ two or 

I \! more concentric ring valves 

with a small lift. These 
valves have given a good 
deal of trouble in some 
cases, in consequence of the 
frequent fracture of the bolts 
which guide and confine the 
rings; but this is only a 
fault of detail which is easily 
remedied, and the principle 
appears to be superior to 
that of any of the other me- 
tallic air pump valves at 
present in common use. 

457. Q. — Are not air pump 
valves now very generally 
made of india rubber ? 

A. — They are almost in- 
variably so made if the en- 
gines are travelling fast, as 
in the case of direct acting 
screw engines, and they are 
very often made of large discs or rings of india rubber, even 
when the engines travel slowly. A very usual and eligible 
arrangement for many purposes is that shown in fig. 41, where 
both foot and delivery valves are situated in the ends of the 
pump, and they, as well as the valve in the bucket are made of 




Trunk Air Pump. Scaled inch to 1 foot. 



DISO VALVES FOPw AIR PUMPS. 



229 



Fi^. 42. 




Penn's Disc Yalye for Air Pump. 

Section. 



Fig. 48. 



India rubber rings closing on a grating. The trunk in the air 
pump enables guide rods to be dispensed with. 

458. Q. — The air pump, when double acting, has of course 
inlet and outlet valves at each end ? 

A. — Yes; and the general arrangement of the valves of 
double acting air pumps, such 
as are usual in direct acting 
screw engines, is that repre- 
sented in the figure of Penn's 
trunk engine already described 
in Chapter I. Each inlet and 
outlet valve consists of a num- 
ber of india rubber discs set 
over a perforated brass plate, 
and each disc is bound down 
by a bolt in the middle, which 
bolt also secures a brass guard 
set above the disc to prevent 
it from rising too high. The 
usual configuration of those 
valves is that represented in 
figs. 42, 43, and 44; figs. 42 
and 43 being a section and 
ground plan of the species of 
valve used by Messrs. Penn, 
and ^g. 44 being a section of 
that used by Messrs. Maudslay. 
It is important in these valves 
to have the india rubber thick, 
— say about an inch thick for 
valves eight inches in diam- 
eter. It is also advisable to 
make the central bolts with a 
nut above and a nut below, and 
to form the bolt with a counter 
sunk neck, so that it will not 
fall down when the top nut is removed. 
II 




PE^^N■s Disc Valvf, for Air Pump. 
Ground Plan. 




Maudslay's Disc Valye for Air Pump. 
Section. 



The lower point of the 



230 CONSTRUCTION OF VALVE PLATES. 

bolt should be riveted over on the nut to prevent it from unscrew- 
ing, and the top end should have a split pin through the point 
for the same pui-pose. The hole through which the bolt passes 
should be tapped, though the bolt is not screwed into it, so 
that if a bolt breaks, a temporary stud may be screwed into the 
hole without the necessity of taking out the whole plate. The 
guard should be large, else the disc may stretch in the central 
hole until it comes over it ; but the guard should not permit 
too much lift of the valve, else a good deal of the water and air 
will return into the pump at the return stroke before the valve 
shuts. Penn's guard is rather small, and Maudslay^s permits 
too much lift. 

459. Q. — What is the proper area through the valve 
gratings ? 

A, — The collective area should be at least equal to the area 
of the pump piston, and the lower edges of the j^erforations 
should be rounded off to afford more free ingress or egress to 
the water. 

460. Q. — Is there much strain thrown on the plates in which 
the valves are set ? 

A, — A good deal of strain ; and in the earlier direct acting 
screw engines these plates were nearly in every case made too 
light. They should be made thick, have strong feathers upon 
them, and be very securely bolted down with split puis at the 
points of the bolts, to prevent them from unscrewing. The 
plate will be very apt to be broken should some of the bolts 
become loose. Of course all the bolts and split pins, as well as 
the plates and guards, must be of brass. 

461. Q. — How are the plates to be taken out should that 
become necessary ? 

A, — They are usually takeA out through a door in the top 
of the hot well provided for that purpose, which door should 
be as large as the plates themselves ; and it is a good precaution 
to cast upon this door — which will be of cast iron — six or eight 
stout projecting feet which will press upon the top of the outlet 
or delivery valve plate when the door is screwed down. The 
upper or delivery valve plate and the lower or foot valve plate 



FAULTS OF DOUBLE ACTING AIR PUMPS. 231 

should have similar feet. A large part of the strain will thug 
be transferred from the plates to the door, which can easily be 
made strong enough to sustain it. It is advisable that the 
plates should lie at an angle so that the shock of the water may 
not come upon the whole surface at once. 

463. Q. — Does the double acting air pump usual in direct 
acting screw engines, produce as good a vacuum as the single 
acting air pump usual in paddle engines ? 

A. — It will do so if properly constructed; but I do not 
know of any case of a double acting air pump, with India rub- 
ber valves, which has been properly constructed. 

463. Q. — What is the fault of such pumps ? 

A. — The pump frequently works by starts, as if at times it 
did not draw at all, and then again on a sudden gorged itself 
with water, so as to throw a great strain upon the working 
parts. The vacuum, moreover, is by no means so good as it 
should 'be, and it is a universal vice of direct acting screw 
engines that the vacuum is defective. I have been at some 
pains to investigate the causes of this imperfection ; and in a 
sugar house engine fitted with pumps like those of a direct 
acting screw engine to maintain a vacuum in the pans, I found 
that a better vacuum was produced when the engine was going 
slowly than when it was going fast ; which is quite the reverse 
of what was to have been expected, as the hot water which had 
to be removed by the condensation of the steam proceeding 
from the pan, was a constant quantity. In this engine, too, 
which was a high pressure one, the irregularities of the engine 
consequent upon the fitful catching of the water by the pump, 
was more conspicuous, as the working of this vacuum pump 
was the only work that the engine had to perform. 

464. Q. — And were you able to discover the cause of these 
irregularities ? 

A. — The main cause of them I found to be the largeness of 
the space left between the valve plates in this class of pumps, 
and out of which there is nothing to press the air or water 
which may be lying there. It consequently happens, that if 
there be the slightest leakage of air into the pump, this air is 



232 CAUSES OF BAD VACUUM. 

merely compressed, and not expelled, by the advance of the air 
pump piston. It exjDands again to its former bulk on the return 
of the pump piston, and prevents the water from entering until 
there is such an accumulation of pressure in the condenser as 
forces the water into the pump, when the air being expelled by 
the water, causes a good vacuum to be momentarily formed in 
the pump when it gorges itself by taking a sudden gulp of 
water. So soon, however, as the pressure falls in the condenser 
and some more air leaks into the pump, the former imperfect 
action recurs and is again redressed in the same violent manner. 

465. Q, — Is this irregular action of the pump the cause of 
the imperfect vacuum ? 

A, — It is one cause. Sometimes one end of the pump will 
alone draw and the other end will be inoperative, although it is 
equally open to the condenser, and this will chiefly take place 
at the stufling box end, where a leakage of air is more likely to 
occur. I find, however, that even when both ends of the pump 
are acting equally and there is no leakage of air at all, the vacuum 
maintained by a double acting horizontal pump with india rub- 
ber valves, is not so good as that maintained by a single acting 
pump of the kind usual in old engines. 

466. Q. — Will you specify more precisely what were the 
results you obtained ? 

A, — When the vacuum pan was exhausted by the pumps 
without any boiling being carried on in the pan, but only a 
little cold water being let into it, and also into the pumps to 
enable them to act in their best manner, it was found that 
whereas with the old pump a vacuum of 114 on the sugar 
boiler's gauge could be readily obtained, equal to about 29^ 
inches of mercury, the lowest that could possibly be got with 
the new horizontal pump was 122 degrees of the sugar boiler's 
gauge, or 29 inches of mercuiy, and to get that the engine must 
not go faster than 10 or 12 strokes per minute. The proj)er 
speed of the engine was 75 strokes i^er minute, but if allowed 
to go at that speed the vacuum fell to 130 of the sugar maker's 
gauge, or 28J inches of mercury. When the steam was let into 
the worms of the pan so as to boil the water in it, the vacuum 



REMEDIES FOR BAD VACUUM. 233 

was 134 at 75 revolutions of the engine, and went down to 132 
at 40 revolutions, but rose again to 135, equal to about 28i 
inches of mercury, at 20 revolutions. 

467. Q. — To what do you attribute the circumstance of a 
better vacuum being got at low speeds than at high speeds ? 

A. — It is difficult to assign the precise reason, but it appears 
to be a consequence of the largeness of the vacant space between 
the valve plates. When the piston of the air pump is drawn 
back, the air contained in this large collection of water will 
cause it to boil up like soda water ; and when the piston of the 
pump is forced forward, this air, instead of being expelled, will 
be again driven into the water. There will consequently be a 
quantity of air in the pump which cannot be got rid of at all, 
and which will impair the vacuum as a matter of course. 

468. Q. — What expedient did you adopt to improve the 
vacuum in the engine to which you have referred ? 

A, — ^I put blocks of wodU on the air pump piston, which at 
the end of its stroke projected between the valve plates and 
forced the water out. I also introduced a cock of water at each 
end of the pump between the valve plates, to insure the presence 
of water at each end of the pump to force the air out. With 
these ameliorations the pump worked steadily, and the vacuum 
obtained became as good as in the old pump. I had previously 
introduced an injection cock into each end of the air pump in 
steam vessels, from which I had obtained advantageous results ; 
and in all horizontal air pumps I would recommend the piston 
and valve plates to be so constructed that the whole of the 
water will be expressed by the piston. I would also recom- 
mend an injection cock to be introduced at each end of the 
pump. 

PUMPS, COCKS, AND PIPES. 

469. Q, — Will you explain the arrangement of the feed 
pump ? 

A. — In steam vessels, the feed pump plunger is generally of 
brass, and the barrel of the pump is sometimes of brass, but 



234 DETAILS OF FEED PUMP — COXSTKUCTION OF COCKS. 

generally of cast iron. There should be a considerable clear- 
ance between the bottom of the plunger and the bottom of the 
barrel, as otherwise the bottom of the barrel may be knocked 
out, should coal dust or any other foreign substance gain admis- 
sion, as it probably would do if the injection water were drawn 
at any time from the bilge of the vessel, as is usually done if the 
vessel springs a leak. The valves of the feed pump, in marine 
engines are generally of the spindle kind, and are most con- 
veniently arranged in a chest, which may be attached in any 
accessible position to the side of the hot well. There are two 
nozzles upon this chest, of which the lower one leads to the 
pump, and the upper one to the boiler. The pipe leading to 
the pump is a suction pipe when the plunger ascends, and a 
forcing pipe when the plunger descends. The plunger in 
ascending draws the water out of the hot well through the low- 
est of the valves, and in descending forces it through the centre 
valve into the space above it, which communicates with the 
feed pipe. Should the feed cock be shut so as to prevent any 
feed water from passing through it, the water will raise the top- 
most valve, which is loaded to a pressure considerably above the 
pressure of the steam, and escape into the hot well. This 
arrangement is neater and less expensive than that of having a 
separate loaded valve on the feed pipe with an overflow through 
the ship's side, as is the more usual practice. 

470. Q, — Will you describe what precautions are to be 
observed in the construction of the cocks used in engines ? 

A, — ^AU the cocks about an engine should be provided with 
bottoms and stuffing boxes, and reliance should never be placed 
upon a single bolt passing through a bottom washer for keeping 
the plug in its place, in the case of any cock communicating 
with the boiler ; for a great strain is thrown upon that bolt if 
the pressure of the steam be high, and if the plug be made with 
much taper ; and should the bolt break, or the threads strip, 
the plug will fly out, and persons standing near may be scalded 
to death. In large cocks, it appears the preferable plan to cast 
the bottoms in ; and the metal of which all the cocks about a 
marine engine are made, should be of the same quality as that 



DETAILS OF THE BLOW-OFF COCKS. 235 

used in the composition of the brasses, and should be without 
lead, or other deteriorating material. In some cases the bot- 
toms of cocks are burnt in with hard solder, but this method 
cannot be depended upon, as the solder is softened and wasted 
away by the hot salt water, and in time the bottom leaks, or is 
forced out. The stuffing box of cocks should be made of ade- 
quate depth, and the gland should be secured by means of four 
strong copper bolts. The taper of blow-off cocks is an impor- 
tant element in their construction ; as, if the taper be too great, 
the plugs will have a continual tendency to rise, which, if the 
packing be slack, will enable grit to get between the faces, 
while, if the taper be too little, the plug will be liable to jam, 
and a few times grinding will sink it so far through the shell 
that the waterways will no longer correspond. One eighth of 
an inch deviation from the perpendicular for every inch in. 
height, is a common angle for the side of the cock, which cor- 
responds with one quarter of an inch difference of diameter in 
an inch of height ; but perhaps a somewhat greater taper than 
this, or one third of an inch difference in diameter for every 
inch of height, is a preferable proportion. The bottom of the 
plug must be always kept a small distance above the bottom of 
the shell, and an adequate surface must be left above and below 
the waterway to prevent leakage. Cocks formed according to 
these directions will be found to operate satisfactorily in practice, 
while they will occasion perpetual trouble if there be any mal- 
formation. 

471. Q. — What is the best arrangement and configuration 
of the blow-off cocks ? 

A. — The blow-off cocks of a boiler are generally placed some 
distance from the boiler ; but it appears preferable that they 
should be placed quite close to it, as there are no means of 
shutting off the water from the pipe between the blow-off cock 
and the boiler, should fracture or leakage there arise. Every 
boiler must be furnished with a blow-off cock of its own, inde- 
pendently of the main blow-off' cocks on the ship's sides, so 
that the boilers may be blown off separately, and may be shut 
off from one another. The preferable arrangement appears to 



236 DETAILS OF THE INJECTION COCKS. 

be, to cast upon each blow-off cock a bend for attaching the 
cock to the bottom of the boiler, and the plug should stand 
about an inch in advance of the front of the boiler, so that 
it may be removed, or re-ground, ^vith facility. The general 
arrangement of the blow-off pipes is to run a main blow-off 
pipe beneath the floor plates, across the ship, at the end of the 
engines, and into this pipe to lead a separate pipe, furnished 
with a cock, from each boiler. The main blow-off pipe, where 
it penetrates the ship's side, is furnished Vrdth a cock : and in 
modern steam vessels Kingston's valves are also used, which 
consist of a spindle or plate valve, fitted to the exterior of the 
ship, so that if the internal pipe or cock breaks, the external 
valve will still be ojoerative. Some expedient of this kind is 
almost necessary, as the blow-off cocks require occasional re- 
grinding, and the sea cocks cannot be re-ground without putting 
the vessel into dock, except by the use of Kingston's valves, or 
some equivalent expedient. 

472. Q. — What is the proper construction and situation of 
the injection cocks, and waste water valves ? 

A. — The sea injection cocks are usually made in the same 
fashion as the sea blow-off cocks, and of about the same size, or 
rather larger. The injection water is generally admitted to the 
condenser by means of a slide valve, but a cock appears to be 
preferable, as it is more easily opened, and has not any dispo- 
sition to shut of its own accord. In paddle vessels the sea 
injection pipes should be put through the ship's sides in advance 
of IJie paddles, so that the water drawn in may not be injuri- 
ously charged with air. The waste water pipe passing from the 
hot well through the vessel's side is provided with a stop valve, 
called the discharge valve, which is usually made of the spindle 
kind, so as to open when the water coming from the air pump 
presses against it. In some cases this valve is a sluice valve, but 
the hot well is then almost sure to be split, if the engine be set 
on without the valve having been opened. The opening of the 
waste water pipe should always be above the load water line, as 
it will otherwise be difficult to prevent leakage through the 
engine into the ship when the vessel is lying in harbor. 



DETAILS OF THE GAUGE COCKS. 237 

473. Q, — What is the best arrangement of gauge cocks and 
glass gauges ? 

A. — Gauge cocks are generally very inartificially made, and 
occasion needless annoyance. They are rarely made with bot- 
toms, or with stuffing boxes, and are consequently, for the most 
part, adorned with stalactites of salt after a short period of ser- 
vice. The water discharged from them, too, from the want of 
a proper conduit, disfigures the front of the boiler, and adds 
to the corrosion in the ash pits. It would be preferable to 
combine the gauge cocks appertaining to each boiler into 
a single upright tube, connected suitably with the boiler, 
and the water flowing from them could be directed downward 
into a funnel tube communicating with the bilge. The cocks 
of the glass tubes, as well as of the gauge cocks, should be fur- 
nished with stuffing boxes and with bottoms, unless the water 
enters through the bottom of the plug, which in gauge cocks is 
sometimes the case. The glass gauge tubes should always be 
fitted with a cock at each neck communicating with the boiler, 
so that the water and steam may be shut off if the tube breaks ; 
and the cocks should be so made as to admit of the tubes being 
blown through with steam to clear them, as in muddy water 
they will become so soiled that the water cannot be seen. The 
gauge cocks frequently have pipes running up within the boiler, 
to the end that a high water level may be made consistent with 
an easily accessible position of the gauge cocks themselves. 
With the glass tubes, however, this species of arrangement is 
not possible, and the glass tubes must always be placed in the 
position of the water level. 

474. Q. — What is the proper material of the pipes in steam 
vessels ? 

^.— Most of the pipes of marine engines should be made of 
copper. The steam pipes may be of cast iron, if made very 
strong, but the waste water pipes should be of copper. Cast 
iron blow-off pipes have in some cases been employed, but they 
are liable to fracture, and are dangerous. The blow-off and 
feod pipes should be of copper, but the waste steam pipe may 
be of galvanized iron. Every pipe passing through the ship's 



238 HOW TO FIT PIPES WHICH PIERCE THE SHIP. 

side, and every pipe fixed at both ends, and liable to be heated 
and cooled, should be furnished with a faucet or expansive 
joint ; and in the case of the cast iron pipes, the part of the 
pipe fitting into the faucet should be turned. In the distri- 
bution of the faucets of the pipes exposed to pressure, care must 
be taken that they be so placed that the parts of the pipe can- 
not be forced asunder, or turned round by the strain, as serious 
accidents have occurred from the neglect of this precaution. 

475. ^.— What is the best mode of making pipes tight 
where they penetrate the ship's side ? 

A. — In wooden vessels the pipes where they pierce the ship's 
side, should be made tight, as follows : — the hole being cut, a 
short piece of lead pipe, with a broad flange at one end, should 
be fitted into it, the place having been previously smeared with 
white lead, and the pipe should then be beaten on the inside, 
until it comes into close contact all around with the wood. A 
loose flange should next be slipped over the projecting end of 
the lead pipe, to which it should be soldered, and the flanges 
should both be nailed to the timber with scupper nails, white 
lead having been previously spread underneath. This method 
of procedure, it is clear, prevents the possibility of leakage 
down through the timbers ; and all, therefore, that has to be 
guarded against after this precaution, is to prevent leakage into 
the ship. To accomplish this object, let the pipe which it is 
desired to attach be put through the leaden hause, and let the 
space between the pipe and the lead be packed with gasket 
and white lead, to which a little olive oil has been added. The 
pipe must have a flange upon it to close the hole in the ship's 
side ; the packing must then be driven in from the outside, and 
be kept in by means of a gland secured with bolts passing 
through the ship's side. If the pipe is below the water line the 
gland must be of brass, but for the waste water pipe a cast iron 
gland will answer. This method of securing pipes penetrating 
the side, however, though the best for wooden vessels, will, it is 
clear, fail to apply to iron ones. In the case of iron vessels, it 
appears to be the best practice to attach a short iron nozzle, 
projecting inward from the skin, for the attachment of every 



BEST MODE OF FITTING SCEEW PIPE AND SCREW. 239 

pipe below the water line, as tlie copper or brass would waste 
the iron of the skin if the attachment were made in the usual 
way. 

DETAILS OF THE SCEEW AND SCEEW SHAFT. 

476. Q. — What is the best method of fixing the screw upon 
the shaft ? 

A, — The best way is to cut two large grooves in the shaft 
coming up to a square end, and two corresponding grooves or 
key seats in the screw boss opposite the arms. Fit into the 
grooves on the shaft keys with heads, the length of which is 
equal to half the depth of the boss, and with the ends of the 
keys bearing against the ends of the grooves in the shaft. Then 
ship on the propeller, and drive other keys of an equal length 
from the other side of the boss, so that the points of the keys 
will nearly meet in the middle ; next burr up the edge of the 
grooves upon the heads of the keys, to prevent them from work- 
ing back ; and finally tap a bolt into the side of the boss to 
penetrate the shaft. Propellers so fitted will never get slack. 

477. Q. — What is the best way of fitting in the screw pipe 
at tho stern ? 

A. — It should have projecting rings, which should be 
turned ; and cast iron pieces with holes in them, bored out to 
the sizes of these rings, should be secured to the stern frames, 
and the pipe be then shipped through all. Before this is done, 
however, the stern post must be bored out by a template to fit 
the pipe, and the pipe is to be secured at the end to the stern 
post either by a great external nut of cast iron, or by bolts pass- 
ing through the stern post and through lugs on the pipe. The 
pipe should be bored throughout its entire length, and the shaft 
should be turned so as to afford a very long bearing which will 
prevent rapid wear. 

478. Q, — How is the hole formed in the deadwood of the 
ship in which the screw works ? 

A, — A great frame of malleable iron, the size of the hole, is 
first set up, and the plating of the ship is brought to the edge 
cf this hole, and is riveted through the frame. It is important 



240 



MODES OF EECEIYING THE THKUST. 



to secure tliis frame very firmly to the rest of tlie ship, with 
which view it is advisable to form a great palm, like the pahn 
of a vice, on its inner superior corner, which, projecting into the 
ship, may be secured by breast-hook plates to the sides, whereby 
the strain which the screw causes will be distributed over the 
stern, instead of being concentrated on the rivets of the frame. 

479. Q, — Are there several lengths of screw shaft ? 
A, — There are. 

480. Q, — How then are these secured to one another ? 

A, — The best mode of securing the several lengths of shaft 
together is by forging the shafts with flanges at the ends, which 
are connected together by bolts, say six strong bolts in each, 
accurately fitted to the holes. 

481. Q. — How is the thrust of the shaft usually received ? 
A, — In some cases it is received on a number of metal discs 

set in a box containing oil ; and should one of these discs stick 



Fig. 44. 




End of the Screw Shaft of Corked, showing: the mode of receiving 
the Thrust. A, discs ; B, tightening wedge. 

fast from friction, the others will be free to revolve. This ar- 
rangement, which is represented in fig. 44, is used pretty exten- 



DETAILS OF THE EADIAL PADDLE AVIIEEL. 241 

sively, and answers the purpose perfectly. It is of course neces- 
sary that the box in which the discs A are set, shall be strong 
enough to withstand the thrust which the screw occasions. 
Another arrangement still more generally used, is that repre- 
sented in figs. 55 and 56, p. 331. It is a good practice to make 
the thrust pluiamer block with a very long sole in the direction 
of the shaft, so as to obviate any risk of canting or springing 
forward when the strain is applied, as such a circumstance, if 
occurring even to a slight extent, would be very likely to cause 
the bearing to heat. 

482. Q. — Are there not arrangements existing in some ves- 
sels for enabling the screw to be lifted out of the water while the 
vessel is at sea ? 

A. — There are ; but such arrangements are not usual in mer- 
chant vessels. In one form of apparatus the screw is set on a 
short shaft in the middle of a sliding frame, which can be raised 
or lowered in grooves like a window and the screw shaft within 
the ship can be protruded or withdrawn by appropriate mech- 
anism, so as to engage or leave free this short shaft as may be 
required. When the screw has to be lifted, the screw shaft is 
drawn into the vessel, leaving the short shaft free to be raised 
up by the sliding frame, and the frame is raised by long screws 
turned round by a winch purchase on deck. A chain or rope, 
however, is better for the purpose of raising this frame, than 
long screws ; but the frame should in such case be provided 
with pall catches like those of a windlass, which, if the rope 
should break, will prevent the screw from falling. 

DETAILS OF THE PADDLES AND TADDLE SHAFT. 

483. Q. — What are the most important details of the con- 
struction of paddle wheels ? 

A. — The structure of the feathering wheel will be hereafter 
described in connection with an account of the oscillating 
engine ; and it will be expedient now to restrict any account of 
the details to the common radial paddle, as applied to ocean 
steamers. The best plan of making the paddle centres is with 



242 SQUARE EYES FOE CENTRES THE BEST. 

square eyes, and each centre should be secured in its place by 
means of eight thick keys. The shaft should be burred up 
against the head of these keys with a chisel, so as to prevent the 
keys from coming back of their own accord. If the keys are 
wanted to be driven back, this burr must be cut off, and if 
made. thick, and of the right taper, they may then be started 
without difficulty. The shaft must of course be forged with 
square projections on it, so as to be suitable for the application 
of centres with square eyes. Messrs. Maudslay & Co. bore out 
their paddle centres, and turn a seat for them on the shaft, after- 
ward fixing them on the shaft with a single key. This plan is 
objectionable for the two reasons, that it is insecure when new, 
and when old is irremovable. The general practice among the 
London engineers is to fix the paddle arms at the centre to a 
plate by means of bolts, a projection being placed upon the 
plates on each side of the arm, to prevent lateral motion ; but 
this method is inferior in durability to that adopted in the 
Clyde, in which each arm is fitted into a socket by means of a 
cutter — a small hole being left opposite to the end of each 
arm, whereby the arm may be forced back by a drift. 

484. Q. — How are the arms attached to the outside rings ? 
A, — Some engineers join the paddle arms to the outer ring 

by means of bolts ; but unless very carefully fitted, those bolts 
after a time become slack sideways, and a constant working of 
the parts of the wheel goes on in consequence. Sometimes the 
part of the other ring opposite the arm is formed into a mor- 
tise, and the arms are wedged tight in these holes by wedges 
driven in on each side ; but the plan is an expensive one, and 
not satisfactory, as the wedges work loose even though riveted 
over at the jDoint. The best mode of making a secure attach- 
ment of the arms to the ring, consists in making the arms with 
long T heads, and riveting the cross piece to the outer ring 
with a number of rivets, not of the largest size, which would 
weaken the outer ring too much. The best way of securing the 
inner rings to the arms is by means of lugs welded on the arms, 
and to which the rings are riveted. 

485. Q. — AYhat are the scantlings of the paddle floats ? 



MODE OP PREVENTING JOLTING SIDEWAYS. 243 

A, — The paddle floats are usually made either of elm or 
pine ; if of the former, the common thickness for large sea-going 
vessels is about %\ inches ; if of the latter, 3 inches. The floats 
should have plates on both sides, else the paddle arms will be 
very liable to cut into the wood, and the iron of the arms will 
be very rapidly wasted. When the floats have been fresh put 
on they must be screwed up several times before they come to a 
bearing. If this be not done, the bolts will be sure to get slack 
at sea, and all the floats on the weather side may be washed off. 
The bolts for holding on the paddle floats are made extra 
strong, on account of the corrosion to which they are subject ; 
and the nuts should be made large, and should be square, so 
that they may be effectually tightened up, even though their 
corners be worn away by corrosion. It is a good plan to give 
the thread of the paddle bolts a nick with a chisel, after the 
nut has been screwed up, which will prevent the nut from turn- 
ing back. Paddle floats, when consisting of more than one 
board, should be bolted together edgeways, by means of bolts 
running through their whole breadth. The floats should not be 
notched to allow of their projection beyond the outer ring, as, 
if the sides of the notch be in contact with the outer ring, the 
ring is soon eaten away in that part, and the projecting part of 
the float, being unsupported, is liable to be broken off. 

486. §. — Do not the wheels jolt sideways when the vessel 
rolls ? 

A, — It is usual to put a steel plate at each end of the paddle 
shafts tightened with a key, to prevent end play when the 
vessel rolls, but the arrangement is precarious and insufiicient. 
Messrs. Maudslay make their paddle shaft bearings with very 
large fillets in the corner, with the view of diminishing the evil ; 
but it would be preferable to make the bearings of the crank 
shafts spheroidal ; and, indeed, it would probably be an im- 
provement if most of the bearings about the engine were to be 
made in the same fashion. The loose end of the crank pin 
should be made not spheroidal, but consisting of a portion of a 
sphere ; and a brass bush might then be fitted into the crank 
eye, that would completely encase the ball of the pin, and yet 



244 MODE OP PUTTING ENGINES INTO A STEAMER. 

permit the outer end of the paddle shaft to fall without strain- 
ing the pin, the bush being at the same time susceptible of a 
slight end motion. The paddle shaft, where it passes through 
the vessel's side, is usually surrounded by a lead stuflfing box, 
which will yield if the end of the shaft falls ; this stuffing box 
prevents leakage into the ship from the paddle wheels : but it 
is expedient, as a further precaution, to have a small tank on 
the ship's side immediately beneath the stuffing box, with a 
pipe leading down to the bilge to catch and conduct away any 
water that may enter around the shaft. 

487. Q, — How is the outer bearing of the paddle wheels sup- 
plied with tallow ? 

A. — The bearing at the outer end of the paddle shaft is 
sometimes supplied with tallow, forced into a hole in the plum- 
mer block cover, as in the case of water wheels ; but for vessels 
intended to perform long voyages, it is preferable to have a 
pipe leading down to the oil cup above the journal from the 
top of the paddle box, through w hich pipe oil may at any time 
be supplied. 

488. Q. — Will you explain the m.ethod of putting engines 
into a steam vessel ? 

A. — As an illustration of this operation it may be advisable 
to take the case of a side lever engine, and the method of pro- 
ceeding is as follows : — First measure across from the inside of 
paddle bearers to the centre of the ship, to make sure that the 
central line, running in a fore and aft direction on the deck or 
beams, usually drawn by the carpenter, is really in the centre. 
Stretch a line across between the paddle bearers in the direction 
of the shaft ; to this line, in the centre of the ship where the 
fore and aft mark has been made, apply a square with arms six 
or eight feet long, and bring a line stretched perpendicularly 
from the deck to the keelson, accurately to the edge of the 
square : the lower point of the line where it touches the keelson 
will be immediately beneath the marks made upon the deck. 
If this point does not come in the centre of the keelson, it will 
be better to shift it a little, so as to bring it to the centre, alter- 
ing the mark upon the deck correspondingly, provided either 



MODE OF PKEPARING THE KEELSONS. 245 

paddle shaft will admit of this being done — one of the paddle 
brackets being packed behind with wood, to give it an addi- 
tional projection from the side of the paddle bearer. Continue 
the line fore and aft upon the keelson as nearly as can be judged 
in the centre of the ship ; stretch another line fore and aft 
through the mark upon the deck, and look it out of winding 
with the line upon the keelson. Fix upon any two points 
equally distant from the centre, in the line stretched trans- 
versely in the direction of the shaft ; and from those points, as 
centres, and with any convenient radius, sweep across the fore 
and aft line to see that the two are at right angles ; and, if not, 
shift the transverse line a little to make them so. From the 
transverse line next let fall a line upon each outside keelson, 
bringing the edge of the square to the line, the other edge rest- 
ing on the keelson. A point will thus be got on each outside 
keelson perpendicularly beneath the transverse line running in 
the direction of the shaft, and a line drawn between those two 
points will be directly below the shaft. To this line the line 
of the shaft marked on the sole plate has to be brought, care 
being taken, at the same time, that the right distance is pre- 
served between the fore and aft line upon the sole plate, and 
the fore and aft line upon the central keelson. 

489. Q, — Of course the keelsons have first to be properly 
prepared ? 

A. — In a wooden vessel, before any part of the machinery is 
put in, the keelsons should be dubbed fair and straight, and be 
looked out of winding by means of two straight edges. The 
art of placing engines in a ship is more a piece of plain common 
sense than any other feat in engineering, and every man of intel- 
ligence may easily settle a method of procedure for himself. 
Plumb lines and spirit levels, it is obvious, cannot be employed 
on board a vessel, and the problem consists in so placing the 
sole plates, without these aids, that the paddle shaft will not 
stand awry across the vessel, nor be carried forward beyond its 
place by the framing shouldering up more than was expected. 
As a plumb line cannot be used, recourse must be had to a 
square ; and it will signify nothing at what angle with the deck 



246 MODE OF SECUEIXG ENGINES TO THE HULL. 

the keelsons run, so long as the line of the shaft across the keel- 
sons is square down £rom the shaft centre. The sole plates 
being fixed, there is no difficulty in setting the other parts of 
the engine in their proper places upon them. The paddle 
wheels must be hung from the top of the paddle box to enable 
the shaft to be rove through them, and the cross stays between 
the engines should be fixed in when the vessel is afloat. To try 
whether the shafts are in a line, turn the paddle wheels, and try 
if the distance between the cranks is the same at the upper and 
under, and the two horizontal centres ; if not, move the end of 
the paddle shaft up or down, backward or forward, until the 
distance between the cranks at all the four centres is the same. 

490. Q. — In what manner are the engines of a steam vessel 
secured to the hull ? 

A. — The engines of a steamer are secured to the hull by 
means of bolts called holding down bolts, and in wooden ves- 
sels a good deal of trouble is caused by these bolts, which are 
generally made of iron. Sometimes they go through the bot- 
tom of the ship, and at other times they merely go through the 
keelson, — a recess being made in the floor or timbers to admit 
of the introduction of a nut. The iron, however, wears rapidly 
away in both cases, even though the bolts are tinned ; and it 
has been found the preferable method to make such of the bolts 
as pass through the bottom, or enter the bilge, of Muntz's metal, 
or of copper. In a side lever engine, four Muntz's metal bolts 
may be put through the bottom at the crank end of the framing 
of each engine, four more at the main centre, and four more at 
the cylinder, making twelve through bolts to each engine ; and 
it is more convenient to make these bolts with a nut at each 
end, as in that case the bolts may be dropped down from the 
inside, and the necessity is obviated of putting the vessel on 
very high blocks in the dock, in order to give room to put the 
bolts up from the bottom. The remainder of the holding down 
bolts may be of iron, and may, by means of a square neck, be 
screwed into the timber of the keelsons as wood screws — the 
upper part being furnished with a nut which may be screwed 
down upon the sole plate, so soon as the wood screw portion is 



PROPER PROPORTIONS OF BOLTS. 247 

in its place. If the cylinder be a fixed one it should be bolted 
down to the sole plate by as many bolts as are employed to 
attach the cylinder cover, and they should be of copper or brass, 
in any sitimtion that is not easily accessible. 

491. Q. — If the engines become loose, how do you refix 
them? 

A, — It is difficult to fix engines eficctually which have once 
begun to work in the ship, for in time the surface of the keel- 
sons on which the engines bear becomes worn uneven, and the 
engines necessarily rock upon it. As a general rule, the bolts 
attaching the engines to the keelsons are too few and of too 
large a diameter : it would be preferable to have smaller bolts, 
and a greater number of them. In addition to the bolts going 
through the keelsons or the vessel's bottom, there should be a 
large number of wood screws securing the sole plate to the keel- 
son, and a large number of bolts securing the various parts of 
the engine to the sole plate. In iron vessels, holding down 
bolts passing through the bottom are not expedient ; and there 
the engine has merely to be secured to the iron plate of the 
keelsons, which are made hollow to admit of a more effectual 
attachment. 

492. Q. — What are the proper proportions of bolts ? 

A. — In well formed bolts, the spiral groove penetrates about 
one twelfth of the diameter of the cylinder round which it 
winds, so that the diameter of the solid cylinder which remains 
is five sixths of the diameter over the thread. If the strain to 
which iron may be safely subjected in machinery is one fifteenth 
of its utmost strength, or 4,000 lbs. on the square inch, then 
2,180 lbs. may be sustained by a screw an inch in diameter, 
at the outside of the threads. The strength of the holding 
down bolts may easily be computed, when the elevating force 
of the piston or main centre is known ; but it is expedient very 
much to exceed this strength in practice, on account of the 
elasticity of the keelsons, the liability to corrosion, and other 
causes. 



248 TEACTIYE FORCE OX RAILWAYS. 



THE LOCOMOTIVE ENGINE. 

493. Q. — What is the amount of tractive force requisite to 
draw carnages on railways ? 

A. — Upon well formed railways with carriages of good con- 
struction, the average tractive force required for low speeds is 
about 7^ lbs. per ton, or g^th of the load, though in some ex- 
perimental cases, where particular care was taken to obtain a 
favorable result, the tractive force has been reduced as low 
as j^o-t^ of the load. At low speeds the whole of the tractive 
force is expended in overcoming the friction, which is made up 
partly of the friction of attrition in the axles, and partly of the 
rolling friction, or the obstruction to the rolling of the wheels 
upon the rail. The rolling friction is very small when the sur- 
faces are smooth, and in the case of railway carriages does not 
exceed foVo^^^ ^^ ^^^ load; whereas the draught on common 
roads of good construction, which is chiefly made up of the 
rolling friction, is as much as Jg^th of the load. 

494. Q. — In reference to friction you have already stated that 
the friction of iron sliding upon brass, which has been oiled 
and then wiped dry, so that no film of oil is interposed, is 
about y\th of the pressure, but that in machines in actual 
operation, where there is a film of oil between the rubbing sur- 
faces, the friction is only about one third of this amount, or g^^d 
of the weight. How then can the tractive resistance of loco- 
motives at low speeds, which you say is entirely made up of 
friction, be so little as ^ Jo th of the weight ? 

A. — I did not state that the resistance to traction was jJoth 
of the weight upon an average — to which condition the answer 
given to a xDrevious question must be understood to apply — but 
I stated that the average traction was about 3^0^^ ^^ the load, 
which nearly agrees with my former statement. If the total 
friction be ^Jo^^ ^^ ^^^ \02i6.^ and the rolling friction be jVoo*^ 
of the load, then the friction of attrition must be 4r,9th of the 
load ; and if the diameter of the wheels be 36 in., and the di- 
ameter of the axles be 3 in., which are common proportions, the 
friction of attrition must be increased in the proportion of 36 to 



EXPENSIVENESS OF HIGH SPEEDS. 249 

3, or 12 times, to represent tlie friction of the rubbing surface 
when moving with the velocity of the carriage. 4V9ths are 
about a^jth of the load, which does not differ much from the 
proportion of g^d as previously determined. 

495. Q. — What is the amount of adhesion of the wheels 
upon the rails ? 

A, — The adhesion of the wheels upon the rails is about Jth 
of the weight when the rails are clean, or either perfectly wet or 
perfectly dry ; but when the rails are half wet or greasy, the 
adhesion is not more than j'^th or J^^h of the weight or pressure 
upon the wheels. The weight of a locomotive of modern con- 
struction varies from 20 to 25 tons. 

496. Q. — And what is its cost and average performance ? 
A. — The cost of a common narrow gauge locomotive, of 

average power, varies from 1,900?. to 2,200?. ; it will run on an 
average 130 miles per day, at a cost for repairs of 2id. per 
mile ; and the cost of locomotive power, including repairs, 
wages, oil, and coke, does not much exceed 6d. j^er mile run, on 
economically managed railways. This does not include a sink- 
ing fund for the renewal of the engines when worn out, which 
may be taken as equivalent to 10 per cent, on their original 
cost. 

497. Q. — Does the expense of traction increase much with 
an increased speed ? 

A, — Yes ; it increases very rapidly, partly from the undula- 
tion of the earth when a heavy train passes over it at a high 
velocity, but chiefly from the resistance of the atmosphere and 
blast pipe, which constitute the greatest of the impediments to 
motion at high speeds. At a speed of 30 miles an hour, the 
atmospheric resistance has been found in some cases to amount 
to about 12 lbs. a ton ; and in side winds the resistance even 
exceeds this amount, partly in consequence of the additional 
friction caused from the flanges of the wheels being forced 
against the rails, and partly because the wind catches to a cer- 
tain extent the front of every carriage, whereby the efficient 
breadth of each carriage, in giving motion to the air in the direc- 
tion of the train, is very much increased. At a speed of 30 miles 



250 INCKEASED EESISTAKCE WITH HIGH SPEED. 

an liour, an engine evaporating 200 cubic feet of water in the 
hour, and therefore exerting about 200 horses power, will draw 
a load of 110 tons. Taking the friction of the train at 7-J^ lbs. 
per ton, or 825 lbs. operating at the circumference of the driving 
wheel — which, with 5 ft. 6 in. wheels, and 18 in. stroke, is 
equivalent to 4,757 lbs. upon the piston — and taking the resist- 
ance of the blast pipe at 6 lbs. per square inch of the pistons, 
and the friction of the engine unloaded at 1 lb. per square inch, 
which, with pistons 12 in. in diameter, amount together to 
1,582 lbs., and reckoning the increased friction of the engine 
due to the load at ^th of the load, as in some cases it has been 
found experimentally to be, though a much less proportion than 
this would probably be a nearer average, we have 7018*4 lbs. 
for the total load upon the pistons. At 30 miles an hour the 
speed of the pistons will be 457*8 feet per minute, and 7018*4 
lbs. multiplied by 457*8 ft. per minute, are equal to 3213023*5 
lbs. raised one foot high in the minute, which, divided by 
33,000, gives 97*3 horses power as the power which would draw 
110 tons upon a railway at a speed of 30 miles an hour, if there 
were no atmospheric resistance. The atmospheric resistance is 
at the rate of 12 lbs. a ton, with a load of 110 tons, equal to 
1,320 lbs., moving at a speed of 30 miles an hour, which, when 
reduced, becomes 105*8 horses power, and this, added to 97*3, 
makes 203*1, instead of 200 horses power, as ascertained by a 
reference to the evaporative power of the boiler. This amount 
of atmospheric resistance, however, exceeds the average, and in 
some of the experiments for ascertaining the atmospheric resist- 
ance, a part of the resistance due to the curves and irregulari- 
ties of the line has been counted as part of the atmospheric 
resistance. 

498. Q, — Is the resistance per ton of the engine the same as 
the resistance per ton of the train ? 

A. — No ; it is more, since the engine has not merely the re- 
sistance of the atmosphere and of the wheels to encounter, but 
the resistance of the machinery besides. According to Mr. 
Gooch's experiments upon a train weighing 100 tons, the resist- 
ance of the engine and tender at 13*1 miles per hour was found 



RESISTANCES AT DIFFERENT SPEEDS. 251 

by tlie indicator to be 12*38 lbs. ; tlie resistance per ton of the 
train, as ascertained by the dynamometer, was at the same 
speed 7'56 lbs., and the average resistance of locomotive and 
train was 9*04 lbs. At 20-2 miles per hour these resistances 
respectively became 19'0, 8*19, and 12'2 lbs. At 44*1 miles per 
hour the resistances became 34-0, 21*10, and 25*5 lbs., and at 
57*4 miles an hour they became 35*5, 17*81, and 23*8 lbs. 

499. Q. — Is it not maintained that the resistance of the atmo- 
sphere to the progress of railway trains increases as the square 
of the velocity ? 

A. — The atmospheric resistance, no doubt, increases as the 
square of the velocity, and the power, therefore, necessary to 
overcome it will increase as the cube of the velocity, since in 
doubling the speed four times, the power must be expended 
in overcoming the atmospheric resistance in half the time. At 
low speeds, the resistance does not increase very rapidly ; but 
at high speeds, as the rapid increase in the atmospheric re- 
sistance causes the main resistance to be that arising from the 
atmosphere, the total resistance will vary nearly as the square 
of the velocity. Thus the resistance of a train, including 
locomotive and tender, will, at 15 miles an hour, be about 9*3 
lbs. per ton ; at 30 miles an hour it will be 13*2 lbs. per ton ; 
and at 60 miles an hour, 29 lbs. per ton. If we suppose the same 
law of progression to continue up to 120 miles an hour, the 
resistance at that speed will be 92*2 lbs. per ton, and at 240 
miles an hour the resistance will be 344*8 lbs. per ton. Thus, 
in doubling the speed from 60 to 120 miles per hour, the resist- 
ance does not fall much short of being increased fourfold, and 
the same remark applies to the increase of the speed from 120 
to 240 miles an hour. These deductions and other deductions 
from Mr. Gooch's experiments on the resistance of railway 
trains, are -fully discussed by Mr. Clark, m his Treatise on rail- 
way machinery, who gives the following rule for ascertaining 
the resistance of a train, supposing the hne to be in good order, 
and free from curves : — To find the total resistance of the en- 
gine, tender, and train in pounds per ton, at any given speed. 
Square the speed in miles per hour ; divide it by 171, and add 



252 LAW OF SQUARES AND CUBES RECONCILED. 

8 to the quotient. The result is the total resistance at the rails 
in lbs. per ton. 

500. Q. — How comes it, that the resistance of fluids increases 
as the square of the velocity, instead of the velocity simply ? 

A. — Because the height necessary to generate the velocity 
with which the moving object strikes the fluid, or the fluid 
strikes the object, increases as the square of the velocity, and 
the resistance or the weight of a column of any fluid varies as 
the height. A falling body, as has been already explained, to 
have acquired twice the velocity, must have fallen through four 
times the height ; the velocity generated by a column of any 
fluid is equal to that acquired by a body falling through the 
height of the column ; and it is therefore clear, that the press- 
ure due to any given velocity must be as the square of that 
velocity, the pressure being in every case as twice the altitude 
of the column. The work done, however, by a stream of air or 
other fluid in a given time, will vary as the cube of the velocity ; 
for if the velocity of a stream of air be doubled, there will not 
only be four times the pressure exerted per square foot, but 
twice the quantity of air will be employed ; and in windmills, 
accordingly, it is found, that the work done varies nearly as the 
cube of the velocity of the wind. If, however, the work done 
by a given quantity of air moving at different speeds be consid- 
ered, it will vary as the squares of the speeds. 

501. Q. — But in a case where there is no work done, and the 
resistance varies as the square of the speed, should not the power 
requisite to overcome that resistance vary as the square of the 
speed ? 

A, — It should if you consider the resistance over a given dis- 
tance, and not the resistance during a given time. Supposing 
the resistance of a railway train to increase as the square of the 
speed, it would take four times the power, so far as atmospheric 
resistance is concerned, to accomplish a mile at the rate of 60 
miles an hour, that it would take to accomplish a mile at 30 
miles an hour ; but in the former case there would be twice the 
number of miles accomplished in the same time, so that when 
the velocity of the train was doubled, we should require an 



CONSTEUCTION OF THE FBAMING. 253 

fingine that was capable of overcoming four times the resistance 
at twice the speed, or in other words, that was capable of 
exerting eight times the power, so far as regards the element of 
atmospheric resistance. We know by experience, however, that 
it is easier to attain high speeds on railways than in steam ves- 
sels, where the resistance does increase nearly as the square of 
the speed. 

502. Q. — Will you describe generally the arrangement of a 
locomotive engine ? 

A, — The boiler and engine are hung upon a framework set 
on wheels, and, together with this frame or carriage, constitute 
what is commonly called the locomotive. Behind the locomo- 
tive runs another carriage, called the tender, for holding coke 
and water. A common mode of connecting the engine and 
tender is by means of a rigid bar, with an eye at each end 
through which pins are passed. Between the engine and ten- 
der, however, buffers should always be interposed, as their 
pressure contributes greatly to prevent oscillation and other 
irregular motions of the engine. 

503. Q. — How is the framing of a locomotive usually con- 
structed ? 

A. — All locomotives are now made with the framing which 
supports the machinery situated within the wheels ; but for 
some years a vehement controversy was maintained respecting 
the relative merits of outside and inside framing, which has ter- 
minated, however, in the universal adoption of the inside fram- 
ing. It is difficult, in engines intended for the narrow gauge, 
to get cylinders within the framing of sufficient diameter to 
meet the exigencies of railway locomotion ; by casting both 
cylinders in a piece, however, a considerable amount of room 
may be made available to increase their diameters. It is very 
desirable that the cyliaders of locomotives should be as large as 
possible, so that expansion may be adopted to a large extent ; 
and with any given speed of piston, the power of an engine 
either to draw heavy loads, or achieve high velocities, will be 
increased with every increase of the dimensions of the cylinder. 
The framing of locomotives, to which the bpiler £^nd machinery 
12 



254 COXSTEUCTION OF THE SPRINGS. 

are attached, and whicli rests upon the springs situated above 
the axles, is formed generally of malleable iron, but in some 
engines the side frames consist of oak with iron plates riveted 
on each side. The guard plates are in these cases generally of 
equal length, the frames being curved upward to pass over the 
driving axle. Hard cast iron blocks are riveted between the 
guard plates to serve as guides for the axle bushes. The side 
frames are connected across the ends, and cross stays are intro- 
duced beneath the boiler to stiffen the frame sideways, and pre- 
vent the ends of the connecting or eccentric rods from falling 
down if they should be broken. 

504. Q. — What is the nature and arrangement of the springs 
of locomotives ? 

A. — The springs are of the ordinary carriage kind, with 
plates connected at the centre, and allowed to slide on each 
other at their ends. The upper plate terminates in two eyes, 
through each of which passes a pin, which also passes through 
the jaws of the bridle, connected by a double threaded screw to 
another bridle, which is jointed to the framing ; the centre of 
the spring rests upon the axle box. Sometimes the springs are 
placed between the guard plates, and below the framing which 
rests upon their extremities. One species of springs which has 
gained a considerable introduction, consists of a number of flat 
steel plates with a piece of metal or other substance interposed , 
between them at the centre, leaving the ends standing apart. 
It would be preferable, perhaps, to make the plates of a com- 
mon spring with different curves, so that the leaves, though in 
contact at the centre, would not be in contact with the ends 
with light loads, but would be brought into contact gradually, 
as the strain comes on : a spring would thus be obtained that 
was suitable for all loads. 

'505. Q. — What is the difference between inside and outside 
cylinder engines ? 

A. — Outside cylinders are so designated when placed upon 
the outside of the framing, with their coimecting rods operating 
upon pins in the driving wheels ; while the inside cylinders 



ADVANTAGES OF FOUK AND SIX WHEELS. 255 

are situated within tlie framing, and tlie connecting rods attach 
themselves to cranks in the driving axle. 

506. Q, — Whether are inside or outside cylinder engines to 
be preferred ? 

A. — A diversity of opinion obtains as to the relative merits 
of outside and inside cylinders. The chief objection to outside 
cylinders is, that they occasion a sinuous motion in the engine 
which is apt to send the train off the rails ; but this action may 
be made less perceptible or be remedied altogether, by placing 
a weight upon one side of the wheels, the momentum of which 
will just balance the momentum of the piston and its connec- 
tions. The sinuous or rocking motion of locomotives is trace- 
able to the arrested momentum of the piston and its attach- 
ments at every stroke of the engine, and the effect of the 
pressure thus created will be more operative in inducing 
oscillation the farther it is exerted from the central line of the 
engine. If both cylinders were set at right angles in the centre 
of the carriage, and the pistons were both attached to a central 
crank, there would be no oscillation produced ; or the same effect 
would be realized by placing one cylinder in the centre of the 
carriage, and two at the sides — the pistons of the side cylinders 
moving simultaneously : but it is impossible to couple the pis- 
ton of an upright cylinder direct to the axle of a locomotive, 
without causing the springs to work up and down with every 
stroke of the engine : and the use of three cylinders, though 
adopted in some of Stephenson's engines, involves too much 
complication to be a beneficial innovaition. 

507. Q. — Whether are four-wheeled or six-wheeled engines 
preferable ? 

A, — Much controversial ingenuity has been expended upon 
the question of the relative merits of the four and six-wheeled 
"engines ; one party maintaining that four-wheeled engines are 
most unsafe, and the other that six-wheeled engines are unme- 
chanical, and are more likely to occasion accidents. The four- 
wheeled engines, however, appear to have been charged with 
faults that do not really attach to them when properly con- 
structed ; for it by no means follows that if the axle of a four- 



256 SOME SIX-WHEELED ENGINES PITCH DANGEROUSLY. 

wheeled engine breaks, or even altogether comes away, that the 
engine must fall down or run off the line ; inasmuch as, if the 
engine be properly coupled with the tender, it has the tender to 
sustain it. It is obvious enough, that such a connection may be 
made between the tender and the engine, that either the fore 
or hind axle of the engine may be taken away, and yet the 
engine will not fall down, but will be kept up by the support 
which the tender affords ; and the arguments hitherto paraded 
against the four-wheeled engines are, so far as regards the ques- 
tion of safety, nothing more than arguments against the exist- 
ence of the suggested connection. It is no doubt the fact, that 
locomotive engines are now becoming too heavy to be capable 
of being borne on four wheels at high speeds without injury to 
the rails ; but the objection of damage to the rails applies with 
at least equal force to most of the six- wheeled engines hitherto 
constructed, as in those engines the engineer has the power of 
putting nearly all the weight upon the driving wheels ; and if 
the rail be wet or greasy, there is a great temptation to increase 
the bite of those wheels by screwing them down more firmly 
upon the rails. A greater strain is thus thrown upon the rail 
than can exist in the case of any equally heavy four-wheeled 
engine ; and the engine is made very unsafe, as a pitching mo- 
tion will inevitably be induced at high speeds, when an engine 
is thus poised upon the central driving wheels, and there will 
also be more of the rocking or sinuous motion. Locomotives, 
however, intended to achieve high speeds or to draw heavy 
loads, are now generally made with eight wheels, and in some 
cases the driving wheels are placed at the end of the engine 
instead of in the middle. 

508. Q. — As the question of the locomotive boiler has been 
already disposed of in discussing the question of boilers in gen- 
eral, it now only remains to inquire into the subject of the 
engine, and we may commence with the cylinders. Will you 
state the arrangement and construction of the cylinders of a 
locomotive and their connections ? 

A. — The cylinders are placed in the same horizontal plane as 
the axle of the driving wheels, and the connecting rod which ig 



ARKANGEMENT OF THE CYLINDEES. 257 

attaclied to tlie piston rod engages either a crank in tlie driving 
axle or a pin in the driving wheel, according as the cylinders 
are inside or outside of the framework. The cylinders are 
generally made an inch longer than the stroke, or there is half 
an inch of clearance at each end of the cylinder, to permit the 
springs of the vehicle to act without causing the piston to strike 
the top or bottom of the cylinder. The thickness of metal of 
the cylinder ends is usually about a third more than the thick- 
ness of the cylinder itself, and both ends are generally made 
removable. The priming of the boiler, when it occurs, is very 
injurious to the cylinders and valves of locomotives, especially 
if the water be sandy, as the grit carried over by the steam 
wears the rubbing surfaces rapidly away. The face of the 
cylinder on which the valve works is raised a little above the 
metal around it, both to facilitate the operation of forming the 
face and with the view of enabling any foreign substance 
deposited on the face to be pushed aside by the valve into the 
less elevated part, where it may lie without occasioning any 
further disturbance. The valve casing is sometimes cast upon 
the cylinder, and it is generally covered with a door which may- 
be removed to permit the inspection of the faces. In some 
valve casings the top as well as the back is removable, which 
admits of the valve and valve bridle being removed with greater 
facility. A cock is placed at each end of locomotive cylinders, 
to allow the water to be discharged which accumulates in the 
cylinder from priming or condensation ; and the four cocks of 
the two cylinders are usually connected together, so that by 
turning a handle the whole are opened at once. In Stephen- 
son's engines, however, with variable expansion, there is but 
one cock provided for this purpose, which is on the bottom of 
the valve chest. 

509. Q, — What kind of piston is used in locomotives ? 

A, — The variety of pistons employed in locomotives is very 
great, and sometimes even the more complicated kinds are found 
to work very satisfactorily ; but, in general, those pistons which 
consist of a single ring and tongue piece, or of two single rings set 
one above the other, so as to break joint, are preferable to those 



258 ARRAXGEMEXT OF THE PISTON ROD GUIDES. 

wMcli consist of many pieces. In Stephenson's pistons the screws 
were at one time liable to work slack, and the springs to break. 

510. Q. — Will you explain the connection of the piston rod 
with the connecting rod ? 

A. — The piston rods of all engines are now generally either 
case hardened very deeply, or are made of steel ; and in loco- 
motive engines the diameter of the piston rod is about one 
seventh of the diameter of the cylinder, and it is formed of 
tilted steel. The cone of the piston rod, by which it is attached 
to the piston, is turned the reverse way to that which is adopted 
in common engines, with the view of making the cutter more 
accessible from the bottom of the cylinder, which is made to 
come off like a door. The top of the piston rod is secured with 
a cutter into a socket with jaws, through the holes of which a 
cross head passes, which is embraced between the jaws by the 
small end of the connecting rod, while the ends of the cross head 
move in guides. Between the piston rod clutch and the guide 
blocks, the feed pump rod joins the cross head in some engines. 

511. Q. — What kind of guides is employed for the end of 
the i^iston rod ? 

A. — The guides are formed of steel plates attached to the 
framing, between which work the guide blocks, fixed on the 
ends of the cross head, which have flanges bearing against the 
inner edges of the guides. Steel or brass guides are better than 
iron ones : Stephenson and Hawthorn attach their guides at 
one end to a cross stay, at the other to lugs on the cylinder 
cover ; and they are made stronger in the middle than at the 
ends. Stout guide rods of steel, encircled by stuffing boxes on 
the ends of the cross head, would probably be found superior 
to any other arrangement. The stuffing boxes might contain 
conical bushes, cut spirally, in addition to the packing, and a 
ring, cut spirally, might be sprung upon the rod and fixed in 
advance of the stuffing box, with lateral play to wipe the rod 
before entering the stuffing box, to prevent it from being 
scratched by the adhesion of dust. 

512. Q. — Is any provision made for keeping the connecting 
rod always of the same length ? 



CONSTRUCTION OF THE CEANKED AXLE. 259 

A. — In every kind of locomotive it is very desirable that the 
length of the connecting rod should remain invariable, in spite 
of the wear of the brasses, for there is a danger of the piston 
striking against the cover of the cylinder if it be shortened, as 
the clearance is left as small as possible in order to economize 
steam. In some engines the strap encircling the crank pin is 
fixed immovably to the connecting rod by dovetailed keys, and 
a bolt passes through the keys, rod, and strap, to prevent the 
dovetailed keys from working out. The brass is tightened by 
a gib and cutter, which is kept from working loose by three 
pinching screws and a cross pin or cutter through the point. 
The effect of this arrangement is to lengthen the rod, but at the 
cross head end of the rod the elongation is neutralized by mak- 
ing the strap loose, so that in tightening the brass the rod is 
shortened by an amount equal to its elongation at the crank 
pin end. The tightening here is also effected by a gib and 
cutter, which is kept from working loose by two pinching screws 
pressing on the side of the cutter. Both journals of the con- 
necting rod are furnished with oil cups, having a small tube in 
the centre with siphon wicks. The connecting rod is a thick 
flat bar, with its edges rounded. 

513. Q, — How is the cranked axle of locomotives con- 
structed ? 

A, — The cranked axle of locomotives is alv/ays made of 
wrought iron, with two cranks forged upon it toward the mid- 
dle of its length, at a distance from each other answerable to 
the distance between the cylinders. Bosses are made on the 
axle for the wheels to be keyed upon, and bearings for the sup- 
port of the framing. The axle is usually forged in two pieces, 
which are afterward welded together. Sometimes the pieces 
for the cranks are put on separately, but the cranks so made are 
liable to give way. In engines with outside cylinders the axles 
are made straight — the crank pins being inserted in the naves 
of the wheels. The bearings to which the connecting rods are 
attached are made with very large fillets in the corners, so as to 
strengthen the axle in that part, and to obviate side play in the 
connecting rod. In engines which have been in use for some 



260 CONSTRUCTION OF THE ECCENTRICS. 

time, however, there is generally a good deal of end j^lay in the 
bearings of the axles themselves, and this slackness contributes 
to make the oscillation of the engine more violent ; but this 
evil may be remedied by making the bearings spheroidal, 
whereby end play becomes impossible. 

514. Q, — How are the bearings of the axles arranged ? 

A. — The axles bear only against the top of the axle boxes, 
which are generally of brass ; but a plate extends underneath 
the bearing, to prevent sand from being thrown upon it. The 
upper part of the box in most engines has a reservoir of oil, 
which is supplied to the journal by tubes with siphon wricks. 
Stephenson uses cast iron axle boxes with brasses, and grease 
instead of oil ; and the grease is fed upon the journal by the 
heat of the bearing melting it, whereby it is made to flow down 
through a hole in the brass. Any engines constructed with 
outside bearings have inside bearings also, which are supported 
by longitudinal bars, which serve also in some cases to support 
the piston guides ; these bearings are sometimes made so as not 
to touch the shafts unless they break. 

515. Q. — How are the eccentrics of a locomotive constructed ? 
A. — In locomotives the body of the eccentric is of cast iron, 

in inside cylinder engines the eccentrics are set on the axle be- 
tween the cranks, and they are put on in two pieces held to- 
gether by bolts ; but in straight axle engines the eccentrics are 
cast in a piece, and are secured on the shaft by means of a key. 
The eccentric, when in two pieces, is retained at its proper angle 
on the shaft by a pinching screw, which is provided with a jam 
nut to prevent it from working loose. A piece is left out of the 
eccentric in casting it to allow of the screw being inserted, and 
the void is afterward filled by inserting a dovetailed piece of 
metal. Stephenson and Hawthorn leave holes in their eccen- 
trics on each side of the central arm, and they apply pinching 
screws in each of these holes. The method of fixing the eccen- 
tric to the shaft by a pinching screw is scarcely sufficiently sub- 
stantial ; and cases are perpetually occurring, when this method 
of attachment is adopted, of eccentrics shifting from their place. 
In the modern engines the eccentrics are forged on the axles. 



CONNECTION OF ECCENTRIC BOD AND VALVE. 261 

516. Q. — How are the eccentric straps constructed ? 

A, — The eccentric hoops are generally of wrought iron, as 
brass hoops are found liable to break. When formed of mal- 
leable iron, one half of the strap is forged with the rod, the 
other half being secured to it by bolts, nuts, and jam nuts. 
Pieces of brass are, in some cases, pinned within the malleable 
iron hoop ; but it appears to be preferable to put brasses with- 
in the hoop to encircle the eccentric, as in the case of any other 
bearing. "When the brass straps are used, the lugs have gen- 
erally nutft on both sides, so that the length of the eccentric rod 
may be adjusted by their means to the proper length ; but it is 
better for the lugs of the hoops to abut against the necks of the 
screws, and, if any adjustment be necessary from the wear of the 
straps, washers can be interposed. In some engines the adjust- 
ment is effected by screwing the valve rod, and the cross head 
through which it passes has a nut on either side of it, by which 
its position upon the valve rod is determined. 

517. Q, — Will you describe the eccentric rod and valve 
levers ? 

A, — In the engines in use before the introduction of the link 
motion, the forks of the eccentric rod were of steel, and the 
length of the eccentric rod was the distance between the centre of 
the crank axle and the centre of the valve shaft ; but in modern 
engines the use of the link motion is universal. The valve lever 
in locomotives is usually longer than the eccentric lever, to in- 
crease the travel of the valve, if levers are employed ; but it is bet- 
ter to connect the valve rod to the link of the link motion with- 
out the intervention of levers. The pins of the eccentric lever 
in the old engines used to wear quickly ; Stephenson used to 
put a ferule of brass on these pins, which being loose, and act- 
ing like a roller, facilitated the throwing in and out of gear, 
and when worn could easily be replaced, so that there was no 
material derangement of the motion of the valve from play in 
this situation. 

518. Q. — What is the arrangement of a starting lever ? 

A. — The starting lever travels between two iron segments, 
and can be fixed in any desired position. This is done by a 



262 AKRANGEMENT OF THE STAKTING GEAR. 

small catcli or bell crank, jointed to the bottom of the handle at 
the end of the lever, and coming up by the side of the handle, 
but pressed out from it by a spring. The smaller arm of this 
bell crank is jointed to a bolt, which shoots into notches, made 
in one of the segments between which the lever moves. By 
pressing the bell crank against the handle of the lever the bolt 
is withdrawn, and the lever may be shifted to any other point, 
when, the spring being released, the bolt flies into the nearest 
notch. 

519. Q. — In what way does the starting handle act on the 
machinery of the engine to set it in motion ? 

A. — Its whole action lies in raising or depressing the link 
of the link motion relatively with the valve rod. If the valve 
rod be attached to the middle of the link, the valve will derive 
no motion from it at all, and the engine will stop. If the 
attachment be slipped to one end of the link the engine will go 
ahead, and if slipped to the other end it will go astern. The 
starting handle merely achieves this change of position. 

520. Q. — Will you explain the operation of setting the valve 
of a locomotive ? 

A. — In setting the valves of locomotives, place the crank in 
the position answerable to the end of the stroke of the piston, 
and draw a straight line, representing the centre line of the 
cylinder, through the centres of the crank shaft and crank pin. 
From the centre of the shaft describe a circle with the diameter 
equal to the throw of the valve ; another circle to represent the 
crank shaft ; and a third circle to represent the path of the 
crank pin. From the centre of the crank shaft, draw a line per- 
pendicular to the centre line of the cylinder and crank shaft, 
and draw another perpendicular at a distance from the first 
equal to the amount of the lap and the lead of the valve : the 
points in which this line intersects the circle of the eccentric 
are the points in which the centre of the eccentric should be 
placed for the forward and reverse motions. When the eccen- 
tric rod is attached directly to the valve, the radius of the 
eccentric, which precedes the crank in its revolution, forms with 
the crank an obtuse angle ; but when, by the intervention of 



EE-SETTING THE ECCENTRICS IF THEY SHIFT. 263 

levers, the valve has a motion opi^osed to that of the eccentric 
rod, the angle contained by the crank and the radius of the 
eccentric must be acute, and the eccentric must follow the 
crank: in other words, with a direct attachment to the valve 
the eccentric is set more than one fourth of a revolution in 
advance of the crank, and with an indirect attachment the 
eccentric is set less than one fourth of a circle behind the crank. 
If the valve were without lead or lap the eccentric w^ould be 
exactly one fourth of a circle in advance of the crank or behind 
the crank, according to the nature of the valve connection ; but 
as the valve would thus cover the port by the amount of the lap 
and lead, the eccentric must be set forward so as to open the 
port to the extent of the lap and lead, and this is effected by 
the plan just described. 

521. Q. — In the event of the eccentrics slipping round upon 
the shaft, which you stated sometimes happens, is it necessary 
to perform the operation of setting the valve as you have just 
described it ? 

^.— If the eccentrics shift upon the shaft, they may be easily 
refixed by setting the valve open the amount of the lead, setting 
the crank at the end of the stroke, and bringing round the 
eccentric upon the shaft till the eccentric rod gears with the 
valve. It would often be troublesome in practice to get access 
to the valve for the purpose of setting it, and this may be dis- 
pensed with if the amount of lap on the valve and the length 
of the eccentric rod be known. To this end draw upon a board 
two straight lines at right angles to one another, and from their 
point of intersection as a centre describe two circles, one repre- 
senting the circle of the eccentric, the other the crank shaft ; 
draw a straight line parallel to one of the diameters, and distant 
from it the amount of the lap and the lead : the points in which 
his parallel intersects the circle of the eccentric are the positions 
of the forward and backward eccentrics. Through these points 
draw straight lines from the centre of the circle, and mark the 
intersection of these lines with the circle of the crank shaft ; 
measure with a pair of compasses the chord of the arc inter- 
cepted between either of these points, and the diameter which 



264 



ARRANGEMENT OF THE FEED PUMPS. 



Fig. 45. 



is at right angles with tlie crank, and the diameters being first 
marked on the shaft itself, then by transferring with the com- 
passes the distance found in the diagram, and marking the 
point, the eccentric may at any time be adjusted without dif- 
ficulty. 

522. Q. — "Will you describe the structure and arrangement 
of t\m feed pumps of locomotive engines ? 

A. — The feed pumps of locomotives are generally made of 
brass, but the plungers are sometimes made of iron, and are 
generally attached to the piston cross head, though in Stephen- 
son's engines they are worked by rods 
attached to eyes on the eccentric hoops. 
There is a ball valve, Jig. 45, between 
the pump and the tender, and two usually 
in the pipe leading from the pump to 
the boiler, besides a cock close to the 
boiler, by which the pump may be shut 
off from the boiler in case of any accident 
to the valves. The ball valves are guided 
by four branches, which rise vertically, 
and join together at the top in a hemis- 
pherical form. The shocks of the ball 
against this cap have in some cases broken 
it after one week's work, fi'om the top 
of the cage having been flat, and the branches not having 
had their junction at the top properly filleted. These valve 
guards are attached in different ways to the pipes ; when one 
occurs at the junction of two pieces of pipe it has a flange, 
which along with the flanges of the pipes and that of the valve 
seat are held together by a union joint. It is sometimes formed 
with a thread at the under end, and screwed into the pipe. The 
balls are cast hollow to lessen the shock, as well as to save the 
metal. In some cases where the feed pump plunger has been 
attached to the cross head, the piston rod has been bent by the 
strain ; and that must in all cases occur, if the communication 
between the pump and boiler be closed when the engine is 
started, and there be no escape valve for the water. 




FEED WATER SHOULD BE ADMITTED LOW DOWN. 265 

523. Q. — Are none but ball valves used in the feed pump ? 
A. — Spindle valves bave in some cases been used instead of 

ball valves, but tbey are more subject to derangement ; but pis- 
ton valves, so contrived as to shut a portion of water in the 
cage when about to close, might be adopted with a great dim- 
inution of the shock. Slide valves might be applied, and would 
probably be found preferable to any of the expedients at present 
in use. In all spindle valves opened and shut rapidly, it is 
advisable to have the lower surface conical, to take off the shock 
of the water ; and a large lift of the valve should be prevented, 
else much of the water during the return stroke of the pump 
will flow out before the valve shuts. 

524. Q. — At what part of the boiler is the feed water ad- 
mitted ? 

A. — The feed pipe of most locomotive engines enters the 
boiler near the bottom and about the middle of its length. In 
Stephenson's engine the water is let in at the smoke box end 
of the boiler, a little below the water level ; by this means the 
heat is more fully extracted from the escaping smoke, but the 
arrangement is of questionable applicability to engines of which 
the steam dome and steam pipe are at the smoke box end, as in 
that case the entering cold water would condense the steam. 

525. Q. — How are the pipes connecting the tender and loco- 
motive constructed, so as to allow of play between the engine 
and tender without leakage ? 

-4. — The pipes connecting the tender with the pumps should 
allow access to the valves and free motion to the engine and 
tender. This end is attained by the use of ball and socket 
joints ; and, to allow some end play, one piece of the pipe slides 
into the other like a telescope, and is kept tight by means of a 
stuffing box. Any pipe joint between the engine and tender 
must be made in this fashion. 

526. Q. — Have you any suggestion to make respecting the 
arrangement of the feed pump ? 

A.— It would be a material improvement if a feed pump was 
to be set in the tender and worked by means of a small engine, 
such as that now used in steam vessels for feeding the boilers. 



266 CONSTRUCTION OF LOCOMOTIVE WHEELS. 

The present action of the feed pumps of locomotives is pre- 
carious, as, if tlie valves leak in the slightest degree, the steam 
or boiling water from the boiler will prevent the pumps from 
drawing. It appears expedient, therefore, that at least one 
pump should be far from the boiler and should, be set among 
the feed water, so that it wdll only have to force. If a pump 
was arranged in the manner suggested, the boiler could still be 
fed regularly, though the locomotive was standing still ; but it 
would be prudent to have the existing pumps still wrought in 
the usual way by the engine, in case of derangement of the 
other, or in case the pump in the tender might freeze. 

527. Q, — Will you explain the construction of locomotive 
wheels ? 

A. — The wheels of a locomotive are always made of mal- 
leable iron. The driving wheels are made larger to increase the 
speed ; the bearing wheels also are easier on the road w^hcn 
large. In the goods engines the driving wheels are smaller 
than in the passenger engines, and are generally coupled to- 
gether. Wheels are made with much variety in their construc- 
tive details : sometimes they are made with cast iron naves, 
with the spokes and rim of wrought iron ; but in the best mod- 
ern wheels the nave is formed of the ends of the spokes welded 
together at the centre. When cast iron naves are adopted, the 
spokes are forged out of flat bars with T-formed heads, and are 
arranged radially in the founder's mould, the cast iron, when 
fluid, being ]Doured among them. The ends of the T heads are 
then welded together to constitute the periphery of the wheel or 
inner tire ; and little wedge-form pieces are inserted where there 
is any deficiency of iron. In some cases the arms are hollow, 
though of wrought iron ; the tire of wrought iron, and the nave 
of cast iron ; and the spokes are turned where they are fitted 
into the nave, and are secured in their sockets by means of cut- 
ters. Hawthorn makes his wheels with cast iron naves and 
wrought iron rims and arms ; but instead of wxlding the arms 
together, he makes palms on their outer end, which are attached 
by rivets to the nm. These rivets, however, unless very care- 
fully formed, are apt to work loose ; and it would probably be 



MODE OF FORMII^TG A WHEEL TIRE. 267 

found an improvement if the palms were to be slightly indented 
into the rim, in cases in which the palms do not meet each other 
at the ends. When the rim is turned it is ready for the tire, 
which is now made of steel. 

528. Q. — How do you find the length of bar necessary for 
forming a tire ? 

A. — To find the proper length of bar requisite for the forma- 
tion of a hoop of any given diameter, add the thickness of the bar 
to the required diameter, and the corresponding circumference in 
the table of circumferences of circles is the leQgth of the bar. If 
the iron be bent edgewise the breadth of the bar must be added 
to the diameter, for it is the thickness of the bar measured radial- 
ly that is to be taken into consideration. In the tires of railway 
wheels, which have a flange on one edge, it is necessary to add 
not only the thickness of the tire, but also two thirds of the depth 
of the flange ; generally, however, the tire bars are sent from the 
forge so curved that the plain edge of the tire is concave, and the 
flange edge convex, while the side which is afterward to be bent 
into contact with the cylindrical surface of the wheel is a plane. 
In this case the addition of the diameter of two thirds of the 
depth of the flange is unnecessary, for the curving of the flange 
edge has the efiect of increasing the real length of the bar. 
When the tire is thus curved, it is only necessary to add the 
thickness of the hoop to the diameter, and then to find the cir- 
cumference from a table ; or the same result will be obtained 
by multiplying the diameter thus increased by the thickness of 
the hoop by 3-1416. 

539. Q. — How are the tires attached to the wheels ? 

A. — The materials for wheel tires are first swaged separate- 
ly, and then welded together under the heavy hammer at the 
steel 'works ; after which they are bent to the circle, welded, 
and turned to certain gauges. The tire is now heated to red- 
ness in a circular furnace ; during the time it is getting hot, the 
iron wheel, turned to the right diameter, is bolted down upon a 
face plate or surface ; the tire expands with the heat, and when 
at a cherry red, it is dropped over the wheel, for which it was 
previously too small, and it is also hastily bolted down to the 



268 FACILITATING PASSAGE ROUND CURVES. 

surface plate ; tlie whole mass is then quickly immersed by a 
swing crane in a tank of water five feet deep, and hauled up 
and down till nearly cold ; the tires are not afterward tempered. 
The tire is attached to the rim with rivets having countersunk 
heads, and the wheel is then fixed on its axle. 

530. Q. — Is it necessary to have the whole tire of steel ? 

A. — It is not indispensable that the whole tire should be of 
steel ; but a dovetail groove, turned out of the tire at the place 
where it bears most on the rail, and fitted with a band of steel, 
will suffice. This band may be put in in pieces, and the expe- 
dient appears to be the best way of repairing a" worn tire ; 
but particular care must be taken to attach these pieces very 
securely to the tire by rivets, else in the rapid revolution of the 
wheel the steel may be thrown out by the centrifugal force. In 
aid of such attachment the steel, after being introduced, is well 
hammered, which expands it sideways until it fills the dovetail 
groove. 

531. §.— Is any arrangement adopted to facilitate the pass- 
age of the locomotive round curves ? 

A, — The tire is turned somewhat conical, to facilitate the 
passage of the en'gine round curves — the diameter of the outer 
wheel being virtually increased by the centrifugal force of the 
engine, and that of the inner wheel being correspondingly 
diminished, whereby the curve is passed without the resistance 
which would otherwise arise from the inequality of the spaces 
passed over by wheels of the same diameter fixed upon the 
same axle. The rails, moreover, are not set quite upright, but 
are slightly inclined inward, in consequence of which the wheels 
must be either conical or slightly dished, to bear fairly upon 
the rails. One benefit of inclining the rails in this way, and 
coning the tires, is that the flange of the wheels is less liable to 
bear against the sides of the rail, and with the same view the 
flanges of all the wheels are made with large fillets in the cor- 
ners. Wheels have been placed loose upon the axle, but they 
have less stability, and are not now much used. Nevertheless 
this plan appears to be a good one if properly worked out. 

533. Q. — Are any precautions taken to prevent engines 



EXPEDIENTS TO CLEAR RAILS OF OBSTACLES. 



269 



from being thrown off the rails by obstructions left upon 
the line ? 

A. — In most engines a bar is strongly attached to the front 
of the carriage on each side, and projects perpendicularly down- 
ward to within a short distance of the rail, to clear away stones 
or other obstructions that might occasion accidents if the engine 
ran over them. 




CHAPTER IX. 



STEAM NAVIGATION. 



RESISTANCE OF VESSELS IN WATER. 

533. Q. — How do you determine the resistance encountered 
by a vessel moving in water ? 

A. — The resistance experienced by vessels moving in water 
varies as the square of the velocity of their motion, or nearly 
so ; and the power necessary to impart an increased velocity 
varies nearly as the cube of such increased velocity. To double 
the velocity of a steam vessel, therefore, will require four times 
the amount of tractive force, and as that quadrupled force must 
act through twice the distance in the same time, an engine 
capable of exerting eight times the original power wiU be 
required,* 

534. Q. — In the case of a board moving in water in the man- 
ner of a paddle float, or in the case of moving water impinging 
on a stationary board, what vrill be the pressure produced by 
the impact ? 

* This statement supposes that there is no difference of level between the 
water at the bow and the water at the stern. In the experiments on the steamer 
Pelican, the resistance was found to vary, as the 2.2Sth power of the velocity, but 
the deviation from the recognized law was imputed to a ditference in the level of 
the water at the bow and stern. 



RESISTANCE OF VESSELS MOVING IN WATER. 271 

A, — The pressure produced upon a flat board, by striking 
water at right angles to the surface of the board, will be equal 
to the weight of a column of water having the surface struck as 
a base, and for its altitude twice the height due to the velocity 
with which the board moves through the water. If the board 
strike the water obliquely, the resistance will be less, but no very 
reliable law has yet been discovered to determine its amount. 

535. Q. — Will not the resistance of a vessel in moving 
through the water be much less than that of a flat board of 
the area of the cross section ? 

A, — It will be very much less, as is manifest from the com- 
paratively small area of paddle board, and the small area of the 
circle described by the screw, relatively with the area of the 
immersed midship section of the vessel. The absolute speed of 
a vessel, with any given amount of power, will depend very 
much upon her shape. 

536. Q, — In what way is it that the shape of a vessel influ- 
ences her speed, since the vessels of the same sectional area must 
manifestly put in motion a column of wat6r of the same magni- 
tude, and with the same velocity ? 

A, — A vessel will not strike the water with the same velo- 
city w^hen the bow lines are sharp as when they are otherwise ; 
for a very sharp bow has the efiect of enabling the vessel to 
move through a great distance, while the particles of water are 
moved aside but a small distance, or in other words, it causes 
the velocity with which the water is moved to be very small 
relatively with the velocity of the vessel ; and as the resist-ance 
increases as the square of the velocity with which the water is 
moved, it is conceivable enough in what way a sharp bow may 
diminish the resistance. 

537. Q. — Is the whole power expended in the propulsion 
of a vessel consumed in moving aside the water to enable the 
vessel to pass ? 

A. — By no means ; only a portion, and in well-formed vessels 
only a small portion, of the power is thus consumed. In the 
majority of cases, the greater part of the power is expended in 
overcoming the friction of the water upon the bottom of the 



272 PEOPER FORM OF THE WxVTER LINES. 

vessel ; and the problem chiefly claiming consideration is, in 
what way we may diminish the friction. 

538. ().— Does the resistance produced by this friction in- 
crease with the velocity ? 

A. — It increases nearly as the square of the velocity. At 
two nautical miles per hour, the thrust necessary to overcome the 
friction varies as the 1*823 power of the velocity ; and at eight 
nautical miles per hour, the thrust necessary to overcome the 
friction varies as the 1*713 power of the velocity. It is hardly 
j)roper, perhaps, to call this resistance by the name of friction ; 
it is partly, perhaps mainly, due to the viscidity or adhesion 
of the water. 

539. Q, — ^Perhaps at high velocities this resistance may 
become less ? 

A. — That appears very probable. It may happen that at 
high velocities the adhesion is overcome, so that the water is 
dragged off the vessel, and the friction thereafter follows the 
law which obtains in the case of solid bodies. But any such 
conclusion is mere speculation, since no experiments illustrative 
of this question have yet been made. 

540. §. — Will a vessel experience more resistance in moving 
in salt water than in moving in fresh ? 

A, — If the immersion be the same in both cases a vessel will 
experience more resistance in moving in salt water than in 
moving in fresh, on account of the greater density of salt water ; 
but as the flotation is proportionably greater in the salt water 
the resistance will be the same with the same weight carried. 

541. Q, — Discarding for the present the subject of friction, 
and looking merely to the question of bow and stem resistance, 
in what manner should the hull of a vessel be formed so as to 
make these resistances a minimum ? 

A, — The hull should be so formed that the water, instead of 
being away driven forcibly from the bow, is opened gradually, so 
that every particle of water may be moved aside slowly at first, 
and then faster, like the ball of a pendulum, until it reaches 
the position of the midship frame, at which point it will have 
come to a state of rest, and then again, Uke a returning pendu- 



EXPERIMENTS ON THE RESISTANCE OF VESSELS. 273 

lum, vibrate back in the same way, until it comes to rest at the 
stern. It is not difficult to describe mechanically the line 
which the water should pursue. If an endless web of paper be 
put into uniform motion, and a pendulum carrying a pencil or 
brush be hung in front of it, then such pendulum will trace on 
the paper the proper water line of the ship, or the line which 
the water should pursue in order that no power may be lost 
except that which is lost in friction. It is found, however, in 
practice, that vessels formed with water lines on this principle 
are not much superior to ordinary vessels in the facility with 
which they pass through the water : and this points to the con- 
clusion that in ordinary vessels of good form, the amount of 
power consumed in overcoming the resistance due to the 
wave at the bow and the partial vacuity at the stern is not so 
great as has heretofore been supposed, and that, in fact, the 
main resistance is that due to the friction. 

EXPERIMENTS ON THE RESISTANCE OF VESSELS. 

■ 542. Q. — Have experiments been made to determine the 
resistance which steam vessels experience in moving through 
the waters ? 

A. — Experiments have been made both to determine the 
relative resistance of different classes of vessels, and also the 
absolute resistance in pounds or tons. The first experiments 
made upon this subject were conducted by Messrs. Boulton 
and Watt, and they have been numerous, long continued, and 
carefully performed. These experiments were made upon pad- 
dle vessels. 

543. Q. — Will you recount the chief results of these experi- 
ments ? 

A. — The purpose of the experiments was to establish a coeffi- 
cient of performance, which with any given class of vessel would 
enable the speed, which would be obtained with any given 
power, to be readily predicted. This coefficient was obtained 
by multiplying the cube of the velocity of the vessels experi- 
mented upon, in miles per hour, by the sectional area of the 



274 BOULTON AND WAlT^S EXPERIMENTS 

im:inersed midsliii^ section in square feet, and dividing by the 
numbers of nominal horses power, and this coefficient will be large 
in the proxDortion of the goodness of the shape of the vessel. 

544. Q. — How many experiments were made altogether ? 

A. — There were five different sets of experiments on five 
difierent classes of vessels. The first set of experiments was 
made in 1828, upon the vessels Caledonia, Diana, Eclipse, 
Kingshead, Moordyke, and Eagle — vessels of a similar form and 
all with square bilges and flat floors ; and the result was to 
establish the number 925 as the coefficient of performance of 
such vessels. The second set of experiments was made upon 
the superior vessels Yenus, Swiftsure, Dasher, Arrow, Spitfire, 
Fury, Albion, Queen, Dart, Hawk, Margaret, and Hero — all 
vessels having flat floors and round bilges, where the coefficient 
became 1160. The third set of experiments was made upon the 
vessels Lightning, Meteor, James Watt, Cinderella, Navy Meteor, 
Crocodile, Watersprite, Thetis, Dolphin, Wizard, Escape, and 
Dragon — all vessels with rising floors and round bilges, and the 
coefficient of performance was found to be 1430. The fourth 
set of experiments v/as made in 1834, upon the vessels Magnet, 
Dart, Eclipse, Flamer, Firefly, Ferret, and Monarch, when the 
coefficient of performance was found to be 1580. The fifth set 
of experiments was made upon the Red Rover, City of Canter- 
bury, Heme, Queen, and Prince of Wales, and in the case of 
those vessels the coefficient rose to 2550. The velocity of any 
of these vessels, with any power or sectional area, may be 
ascertained by multiplying the coefficient of its class by the 
nominal horse power, dividing by the sectional area in square 
feet, and extracting the cube root of the quotient, which will be 
the velocity in miles per hour ; or the number of nominal horse 
power requisite for the accomplishment of any required speed 
may be ascertained by multiplying the cube of the required 
velocity in miles per hour, by the sectional area in square feet, 
and dividing by the coefficient : the quotient is the number of 
nominal horse power requisite to realize the speed. 

545. Q. — Seeing, however, that the nominal power does not 
represent an invariable amount of dynamical efficiency, would it 



ON" THE RESISTA]Sr.CE OF STEAM VESSELS. 275 

not be better to make the comparison with reference to the 
actual power ? 

A, — In the whole of the experiments recited, except in the 
case of one or two of the last, the pressure of steam in the 
boiler varied between 2| lbs. and 4 lbs. per square inch, and 
the effective pressure on the piston varied between 11 lbs. and 
13 lbs. per square inch, so that the average ratio of the nominal 
to the actual power may be easily computed ; but it will be 
preferable to state the nominal power of some of the vessels, and 
their actual power as ascertained by experiment. 

546. §.— Then state this. 

A. — Of the Eclipse, the nominal power was 76, and the 
actual power 144*4 horses ; of the Arrow, the nominal power 
was 60, and the actual 119*5 ; Spitfire, nominal 40, actual 64 ; 
Fury, nominal 40, actual 65*6 ; Albion, nominal 80, actual 
135*4 ; Dart, nominal 100, actual 152*4 ; Hawk, nominal 40, 
actual 73 ; Hero, nominal 100, actual 171*4 ; Meteor, nominal 
100, actual 160 ; James Watt, nominal 120, actual 204 ; Water- 
sprite, nominal 76, actual 157*6 ; Dolphin, nominal 140, actual 
238 ; Dragon, nominal 80, actual 131 ; Magnet, nominal 140, 
actual 238 ; Dart, nominal 120, actual 237 ; Flamer, nominal 
120, actual 234 ; Firefly, nominal 52, actual 86*6 ; Ferret, 
nominal 52, actual 88 ; Monarch, nominal 200, actual 378. In 
the case of swift vessels of modern construction, such as the 
Eed Rover, Heme, Queen, and Prince of Wales, the coefficient 
appears to be about 2550 ; but in these vessels there is a still 
greater excess of the actual over the nominal power than in the 
case of the vessels previously enumerated, and the increase in 
the coefficient is consequent upon the increased pressure of the 
steam in the boiler, as well as the superior form of the ship. 
The nominal power of the Red Rover, Heme, and City of Can- 
terbury is, in each case, 120 horses, but the actual power of the 
Red Rover is 294, of the Heme 354, and of the City of Canter- 
bury 306, and in some vessels the excess is still greater ; so that 
with such variations it becomes necessary to adopt a coefficient 
derived from the introduction of the actual instead of the 
nominal power. 



276 BOULTON AND WATt's EXPERIMENTS. 

547. Q. — What will be the average difference between the 
nominal and actual powers in the several classes of vessels you 
have mentioned and the respective coefficients when corrected 
for the actual power ? 

A, — In the first class of vessels experimented upon, the 
actual power was about 1*6 times greater than the nominal 
power ; in the second class, 1*67 times greater ; in the third 
class, 1*7 times greater; and in the fourth, 1-96 times greater; 
while in such vessels as the Red Rover and City of Canterbury, 
it is 2*65 times greater ; so that if we adopt the actual instead 
of the nominal power in fixing the coefficients, we shall have 
554 as the first coefficient, 694 as the second, 832 for the 
third, and 806 for the fourth, instead of 925, 1160, 1430, and 
1580 as previously specified ; while for such vessels as the Red 
Rover, Heme, Queen, and Prince of Wales, we shall have 963 
instead of 2550. These smaller coefficients, then, express the 
relative merits of the dififerent vessels without reference to any 
difference of efficacy in the engines, and it appears preferable, 
with such a variable excess of the actual over the nominal 
power, to employ them instead of those first referred to. From 
the circumstance of the third of the new coefficients being 
gi'eater than the fourth, it appears that the superior result in 
the fourth set of experiments arose altogether from a greater 
excess of the actual over the nominal power. 

548. Q. — These experiments, you have already stated, were 
all made on paddle vessels. Have similar coefficients of per- 
formance been obtained in the case of screw vessels ? 

A. — The coefficients of a greater number of screw vessels 
have been obtained and recorded, but it would occupy too 
much time to enumerate them here. The coefficient of perform- 
ance of the Fairy is 464*8 ; of the Rattler 676*8 ; and of the 
Frankfort 792*3. This coefficient, however, refers to nautical 
and not to statute miles. If reduced to statute miles for the 
purpose of comparison with the previous experiments, the co- 
efficients will respectively become 703, 1033, and 1212 ; which 
indicate that the performance of screw vessels is equal to the 
performance of paddle vessels, but some of the superiority of 



INFLUENCE OF SIZE ON RESISTANCE. 211 

the result may be imputed to the superior size of the screw 
vessels. 



INFLUENCE OF THE SIZE OF VESSELS UPON THEIE SPEED. 

549. Q. — Will large vessels attain a greater speed than small, 
supposing each to be furnished with the same proportionate 
power ? 

A. — It is well known that large vessels furnished with the 
same proportionate power, will attain a greater speed than 
small vessels, as appears from the rule usual in yacht races of 
allowing a certain part of the distance to be run to vessels 
which are of inferior size. The velocity attained by a large 
vessel will be greater than the velocity attained by a small 
vessel of the same mould and the same proportionate power, in 
the proportion of the square roots of the linear dimensions of 
the vessels. A vessel therefore with four times the sectional 
area and four times the power of a smaller symmetrical vessel, 
and consequently of twice the length, will have its speed in- 
creased in the proportion of the square root of 1 to the square 
root of 2, or 1*4 times. 

550. Q. — Will you further illustrate this doctrine by an 
example ? 

A. — The screw steamier Fairy, if enlarged to three times the 
size while retaining the same form, would have twenty-seven 
times the capacity, nine times the sectional area, and nine times 
the power. The length of such a vessel would be 434 feet ; her 
breadth 63 feet 4^ inches ; her draught of water 16^ feet ; her 
area of immersed section 729 square feet ; and her nominal 
power 1080 horses. Now as the lengths of the Fairy and of 
the new vessel are in the proportion of 1 to 3, the speeds will be 
in the proportion of the square root of 1 to the square root of 
3 ; or, in other words, the speed of the large vessel will be 1*73 
times greater than the speed of the small vessel. If therefore 
the speed of the Fairy be 13 knots, the speed of the new vessel 
will be 22*49 knots, although the proportion of power to sec- 
tional area, which is supposed to be the measure of the resist- 
13 



278 SLIP OF PADDLE WHEELS. 

ance, is in both cases precisely the same. If the speed of the 
Fairy herself had to be increased to 22*29 knots, the power 
would have to be increased in the proportion of the cube of 13 
to the cube of 22-49, or 5*2 times, which makes the power neces- 
sary to propel the Fairy at that speed equal to 624 nominal 
horses power. 

STPwUCTUEE AND OPERxiTION OF PADDLE WHEELS. 

551. Q. — Will you describe the configuration and mode of 
action of the paddle wheels in general use ? 

A. — There are two kinds of paddle wheels in extensive use, 
the one being the ordinary radial v/heel, in which the floats are 
fixed on arms radiating from the centre ; and the other the 
feathering wheel, in which each float is hung upon a centre, 
and is so governed by suitable mechanism as to be always kept 
in nearly the vertical position. In the radial wheel there is 
some loss of power from oblique action, whereas in the feather- 
ing wheel there is little or no loss from this cause ; but in every 
kind of paddle there is a loss of power from the recession of the 
water from tha float boards, or the 8lip as it is commonly called ; 
and this loss is the necessary condition of the resistance for the 
propulsion of the vessel being created in a fluid. The slip is 
expressed by the difterence between the speed of the wheel and 
the speed of the vessel, and the larger this diflference is the 
greater the loss of power from slip must be — the consumption 
of steam in the engine being proportionate to the velocity of 
the wheel, and the useful effect being proportionate to the speed 
of the ship. 

552. Q. — The resistance necessary for propulsion will not be 
situated at the circumference of the wheel ? 

A. — In the feathering wheel, where every part of any one 
immerged float moves forward with the same horizontal veloci- 
ty, the pressure or resistance may be supposed to be concen- 
trated in the centre of the float ; whereas, in the common radial 
wheel this cannot be the case, for as the outer edge of the float 
moves more rapidly than the edge nearest the centre of the 



NATUEE OF THE CENTRE OF PKESSURE. 279 

wlieel, the outer part of the float is the most effectual in pro- 
pulsion. The point at which the outer and inner portions of 
the float just balance one another in propelling effect, is called 
the centre of pressure ; and if all the resistances were concen- 
trated in this point, they would have the same effect as before 
in resisting the rotation of the wheel. The resistance upon any 
one moving float board totally immersed in the water will, when 
the vessel is at rest, obviously vary as the square of its distance 
from the centre of motion — ^the resistance of a fluid varying 
with the square of the velocity ; but, except when the wheel is 
sunk to the axle or altogether immersed in the water, it is im- 
possible, under ordinary circumstances, for one float to be total- 
ly immersed without others being immersed partially, whereby 
the arc described by the extremity of the paddle arm will be- 
come greater than the arc described by the inner edge of the 
float ; and consequently the resistance upon any part of the 
float will increase in a higher ratio than the square of its dis- 
tance from the centre of motion — ^the position of the centre of 
pressure being at the same time correspondingly affected. In the 
feathering wheel the position of the centre of pressure of the en- 
tering and emerging floats is continually changing from the 
lower edge of the float — where it is when the float is entering 
or leaving the water — to the centre of the float, which is its 
position when the float is wholly immerged ; but in the radial 
wheel the centre of jDressure can never rise so high as the centre 
of the float. 

553. Q, — All this relates to the action of the paddle when 
the vessel is at rest : will you explain its action when the vessel 
is in motion ? 

A. — When the wheel of a coach rolls along the ground, any 
point of its periphery describes in the air a curve which is 
termed a cycloid ; any point within the periphery traces a pro- 
late or protracted cycloid, and any point exterior to the peri- 
phery traces a curtate or contracted cycloid — the prolate cy- 
cloid partaking more of the nature of a straight line, and the 
curtate cycloid more of the nature of a circle. The action of a 
paddle wheel in the water resembles in this respect that of 



280 NATURE AND DIMENSIONS OF THE ROLLING CIRCLE. 

the wheel of a carriage running along tlie ground : that point 
in the radius of the paddle of which the rotative speed is just 
equal to the velocity of the vessel will describe a cycloid ; 
points nearer the centre, prolate cycloids, and points further 
from the centre, curtate cycloids. The circle described by the 
point whose velocity equals the velocity of the ship, is called 
the rolling circle^ and the resistance due to the difference of 
velocity of the rolling circle and centre of pressure is that which 
operates in the propulsion of the vessel. The resistance upon 
any part of the float, therefore, will vary as the square of its 
distance from the rolling circle, supposing the float to be totally 
immerged ; but, taking into account the greater length of time 
during which the extremity of the paddle acts, whereby the 
resistance will be made greater, we shall not err far in estimat- 
ing the resistance upon any point at the third power of its dis- 
tance from the rolling circle in the case of light immersions, and 
the 2'5 power in the case of deep immersions. 

554. Q. — How is the position of the centre of pressure to be 
determined ? 

A. — With the foregoing assumption, which accords suf- 
ficiently with experiment to justify its acceptation, the position 
of the centre of pressure may be found by the following rule : 
— from the radius of the wheel substract the radius of the roll- 
ing circle ; to the remainder add the depth of the paddle board, 
and divide the fourth power of the sum by four times the 
depth ; from the cube root of the quotient subtract the dif- 
ference between the radii of the wheel and rolling circle, and 
the remainder will be the distance of the centre of pressure from 
the upper edge of the paddle. 

555. Q. — How do you find the diameter of the rolling circle ? 
A. — The diameter of the rolling circle is very easily found, 

for we have only to divide 5,280 times the number of miles per 
hour, by 60 times the number of strokes per minute, to get an 
expression for the circumference of the rolling circle, or the fol- 
lowing rule may be adopted : — divide 88 times the speed of the 
vessel in statute miles per hour, by 3*1416 times the number of 
strokes per minute ; the quotient will be the diameter in feet of 



POSITION OF THE CENTRE OP PRESSURE. 281 

the rolling circle. The diameter of the circle in which the 
centre of pressure moves or the efifective diameter of the wheel 
being known, and also the diameter of the rolling circle, we at 
once find the excess of the velocity of the wheel over the 
vessel. 

556^ Q^ — "Will you illustrate these rules by an example ? 

A. — A steam vessel of moderately good shape, and with 
engines of 200 horses power, realises, with 22 strokes per min- 
ute, a speed of 10*62 miles per hour. To find the diameter of 
the rolling circle, we have 88 times 10*62, equal to 934-66, and 
22 times 3*1416, equal to 69*1152 ; then 934*66 divided by 
69*1152 is equal to 13*52 feet, which is the diameter of the roll- 
ing circle. The diameter of the wheel is 19 ft. 4 in., so that the 
diameter of the rolling circle is about f ds of the diameter of the 
wheel, and this is a frequent proportion. The depth of the 
paddle board is 2 feet, and the difference between the diame- 
ters of the wheel and rolling circle will be 5*8133, which will 
make the diff'erence of their radii 2*9067 ; and adding to this 
the depth of the paddle board, we have 4*9067, the fourth 
power of which is 579*64, which, divided by four times the 
depth of the paddle board, gives us 72*455, the cube root of 
which is 4*1689, which, diminished by the diff'erence of the 
radii of the wheel and rolling circle, leaves 1*2622 feet for the 
distance of the centre of pressure from the upper edge of the 
paddle board in the case of light immersions. The radius of 
the wheel being 9*6667, the distance from the centre of the 
wheel to the upper edge of the float is 7*6667, and adding to 
this 1*2622, we get 8*9299 feet as the radius, or 17*8598 feet as 
the diameter of the circle in which the centre of pressure re- 
volves. With 22 strokes per minute, the velocity of the centre 
of pressure will be 20*573 feet per second, and with 10*62 miles 
per hour for the speed of the vessel, the velocity of the rolling 
circle will be 15*576 feet per second. The effective velocity will 
be the difference between these quantities, or 4*997 feet per 
second. Now the height from which a body must fall by 
gravity, to acquire a velocity of 4*997 feet per second, is about 
•62 feet ; and twice this height, or 1*24 feet, multiplied by 62 J, 



282 EQUIVALENT PRESSURE ON PISTONS. 

wliich is the number of lbs. weight in a cubic foot of water, 
gives 77^ lbs. as the pressure on each square foot of the vertical 
paddle boards. As each board is of 20 square feet of area, and 
there is a vertical board on each side of the ship, the total 
pressure on the vertical paddle boards will be 2900 lbs. 

557. Q. — What pressure is this equivalent to on each square 
inch of the pistons ? 

A, — A vessel of 200 horses power will have two cylinders, 
each 50 inches diameter, and 5 feet stroke, or thereabout. The 
area of a piston of 50 inches diameter is 1963-5 square inches, 
so that the area of the two pistons is 3927 square inches, and 
the piston will move through 10 feet every revolution ; and 
with 22 strokes per minute this will be 220 feet per minute, or 
3'66 feet per second. Now, if the effective velocity of the centre 
of pressure and the velocity of the pistons had been the same, 
then a pressure of 2900 lbs. upon the vertical paddles would 
have been balanced by an equal pressure on the pistons, which 
would have been in this case about -75 lbs. per square inch ; but 
as the effective velocity of the centre of pressure is 4*997 feet 
per second, while that of the pistons is only 3*66 feet per second, 
the pressure must be increased in the proportion of 4*997 to 
3*66 to establish an equilibrium of pressure, or, in other words, 
it must be 1*02 lbs. per square inch. It follows from this inves- 
tigation, that, in radial wheels, the greater part of the engine 
power is distributed among the oblique floats. 

558. Q. — How comes this to be the case ? 

A, — To understand how it happens that more power is ex- 
pended upon the oblique than upon the vertical floats, it is 
necessary to remember that the only resistance upon the vertical 
paddle is that due to the difference of velocity of the wheel and 
the ship ; but if the wheel be supposed to be immersed to its 
axle, so that the entering float strikes the water horizontally, it 
is clear that the resistance on such float is that due to the whole 
velocity of rotation ; and that the resistance to the entering 
float will be the same whether the vessel is in motion or not. 
The resistance opposed to the rotation of any float increases 
from the position of the vertical float — where the resistance is 



PKOPEK PHOPOSTIONS OF A PADDLE WHEEL. 283 

that due to the difference of velocity of the wheel and vessel — 
until it reaches the plane of the axis, supposing the wheel to be 
immersed so far, where the resistance is that due to the whole 
velocit}^ of rotation ; and although in any oblique float the total 
resistance cannot be considered operative in a horizontal direc- 
tion, yet the total resistance increases so rapidly on each side of 
the vertical float, that the portion of it which is operative in the 
horizontal direction, is in all ordinary cases of immersion very 
considerable. In the feathering wheel, where there is little of 
this oblique action, the resistance will be in the proportion of 
the square of the horizontal velocities of the several floats, which 
may be represented by the horizontal distances between them ; 
and in the feathering wheel, the vertical float having the great- 
est horizontal velocity will have the greatest propelling effect. 

559. Q. — Should the floats in feathering wheels enter and 
leave the water vertically ? 

A. — The floats should be so governed by the central crank or 
eccentric, that the entering and emerging floats have a direction 
intermediate between a radius and a vertical line. 

560. Q. — Can you give any practical rules for proportioning 
paddle wheels ? 

A. — A common rule for the pitch of the floats is to allow one 
float for every foot of diameter of the wheel ; but in the case 
of fast vessels a pitch of 2^ feet, or even less, appears preferable, 
as a close pitch occasions less vibration. If the floats be put too 
close, however, the water will not escape freely from between 
them, and if set too far apart the stroke of the entering paddle 
will occasion an inconvenient amount of vibratory motion, 
and there will also be some loss of power. To find the proper 
area of a single float : — divide the number of actual horses 
power of both engines by the diameter of the wheel in feet ; 
the quotient is the area of one paddle board in square feet 
proper for sea going vessels, and the area multiplied by 0-6 will 
give the length of the float in feet. In very sharp vessels, which 
offer less resistance in passing through the water, the area of 
paddle board is usually one-fourth less than the above propor- 
tion, and the proper length of the float may in such case be 



284 BEXEFITS OF LAEGE FLOATS. 

found by multiplying the area by 0-7. In sea going vessels 
about four floats are usually immersed, and in river steamers 
only one or two floats. There is more slip in the latter case, 
but there is also more engine power exerted in the propulsion 
of the ship, from the greater speed of engine thus rendered pos- 
sible. 

561. Q. — Then is it beneficial to use small floats ? 

A. — Quite the contrary. If to permit a greater speed of the 
engine the floats be diminished in area instead of being raised 
out of the water, no appreciable accession to the speed of the 
vessel will be obtained ; whereas there wiU be an increased 
speed of vessel if the accelerated speed of the engine be caused 
by diminishing the diameter of the wheels. In vessels intended 
to be fast, therefore, it is exjoedient to make the wheels small, 
so as to enable the engine to work with a high velocity ; and it 
is expedient to make such wheels of the feathering kind, to 
obviate loss of powder from oblique action. In no wheel must 
the rolling circle fall below the water line, else the entering and 
emerging floats will carry masses of water before them. The 
slip is usually equal to about one-fourth of the velocity of the 
centre of ]3ressure in w^ell proportioned wheels ; but it is desira- 
ble to have the slip as small as is possible consistently with the 
observance of other necessary conditions. The speed, of the 
engine and also the speed of the vessel being fixed, the diameter 
of the rolling circle becomes at once ascertainable, and adding 
to this the slip, we have the diameter of the w^heel. 

COXriGUEATION AND ACTION OF THE SCEEW. 

562. Q. — Will you describe more in detail than you have yet 
done, the configuration and mode of action of the screw pro- 
peller ? 

A. — The ordinary form of screw propeller is represented in 
figs. 46 and 47 ; Jig, 46 being a perspective view, and fig. 47 
an end view, or view such as is seen when looking upon the end 
of the shaft. The screw here represented is one with two arms 
or blades. Some screws have three arms, some four and some 



COI^FIGURATION OF THE SCREW PROPELLER. 285 



Fig. 46. 



Fig. 47. 





Okdinary form op Screw 
Propeller. 



six ; but the screw with two arms is the most usual, and screws 
with more than three arms are not 
now much employed in this country. 
The screw on being put into revolu- 
tion by the engine, preserves a spiral 
path in the water, in which it draws 
itself forward in the same way as a 
screw nail does when turned round 
in a piece of wood, whereas the 
paddle wheel more resembles the ac- 
tion of a cog wheel working in a rack. 

563. Q. — But the screw of a 
steam vessel has no resemblance to 
a screw nail ? 

A. — ^It has in fact a very close resemblance if you suppose only 
a very short piece of the screw nail to be employed, and if you 
suppose, moreover, the thread of the screw to be cut nearly 
into the centre to prevent the wood from stripping. The origin 
nal screw propellers were made with several convolutions of 
screw, but it was found advantageous to shorten them, until 
they are now only made one-sixth of a convolution in length. 

564. Q, — And the pitch you have already explained to be 
the distance in the line of the shaft from one convolution to 
the next, supposing the screw to consist of two or more con- 
volutions ? 

A. — Yes, that is what is meant by the pitch. If a thread 
be wound upon a cylinder with an equal distance between 
the convolutions, it will trace a screw of a uniform pitch ; and 
if the thread be wound upon the cylinder with an increasing 
distance between each convolution, it will trace a screw of an 
increasing pitch. But two or more threads may be wound 
upon the cylinder at the same time, instead of a single thread. 
If two threads be wound upon it they will trace a double- 
threaded screw ; if three threads be wound upon it they will 
trace a treble-threaded screw ; and so of any other number. 
Now if the thread be supposed to be raised up into a very deep 
and thin spiral feather, and the cylinder be supposed to become 



286 



MODE OF APPLYING THE SCREW. 



very small, like the newel of a spiral stair, then a screw will be 
obtained of the kind proper for propelling vessels, except tliat 
only a very short piece of such screw must be employed. What- 
ever be the number of threads wound upon a cylinder, if the 
cylinder be cut across all the threads will be cut. A slice cut 
out of the cylinder will therefore contain a piece of each thread. 
But the threads, in the case of a screw propeller, answer to the 
arms, so that in every screw propeller the number of threads 
entering into the composition of the screw will be the same as 
the number of arms. An ordinary screw with two blades is a 
short piece of a screw of two threads. 

565. Q, — In what part of the ship is the screw usually 
placed ? 

lig. 48. 




A, — In that part of the run of the ship called the dead wood, 
which is a thin and unused part of the vessel just in advance of 
the rudder. The usual arrangement is shown in fig, 48, 
which represents the application to a vessel of a species of 
screw which has the arms bent backwards, to counteract the 



POSITIVE AND NEGATIVE SLIP. 287 

centrifugal motion given to the water wlien tliere is a con- 
siderable amount of slip. 

568. Q. — How is the slip in a screw vessel determined ? 

A. — By comparing the actual speed of the vessel with the 
speed due to the pitch and number of revolutions of the screw, 
or, what is the same thing, the speed which the vessel would 
attain if the screw worked in a solid nut. The difference between 
the actual speed and this hypothetical speed, is the slip. 

567. Q. — In well formed screw propellers what is the amount 
of slip found to be ? 

^.— If the screw be jDroperly proportioned to the resistance 
that the vessel has to overcome, the slip will not be more than 
10 per cent., but in some cases it amounts to 30 per cent., or 
even more than this. In other cases, however, the slip is nothing 
at all, and even less than nothing ; or, in other words the vessel 
jjasses through the water with a greater velocity than if the 
screw were working in a solid nut. 

568. Q. — Then it must be by the aid of the wind or some 
other extraneous force ? 

A, — No ; by the action of the screw alone. 

569. Q. — But how is such a result possible ? 

A. — It appears to be mainly owing to the centrifugal action 
of the screw, which interposes a film or wedge of water between 
the screw itself and the water on which the screw reacts. This 
negative slip, as it is called, chiefly occurs when the pitch 
of the screw is less than its diameter, and when, consequently, 
the velocity of rotation is greater than if a coarser pitch had 
been employed. There is, moreover, in all vessels passing 
through the water with any considerable velocity, a current of 
water following the vessel, in which current, in the case of a 
screw vessel, the screw will revolve ; and in certain cases the 
phenomenon of negative slip may be imputable in part to the 
existence of this current. 

570. Q, — Is the screw propeller as effectual an instrument 
of propulsion as the radial or feathering paddle ? 

A, — In all cases of deep immersion it appears to be quite as 
effectual as the radial paddle, indeed, more so ; but it is scarcely 



288 COMPARISON OF THE SCREW AND PADDLES. 

as effectual as the feathering paddle, with any amount of immer- 
sion, and scarcely as effectual as the common paddle in the case 
of light immersions. 

COMPAEATIYE ADVANTAGES OF PADDLE AND SCPwEW VESSELS. 

571. Q. — Whether do you consider paddle or screw vessels 
to be on the whole the most advantageous ? 

A. — That is a large question, and can only receive a qualified 
answer. In some cases the use of paddles is indispensable, as, 
for example, in the case of river vessels of a limited draught of 
water, where it would not be possible to get suflacient depth 
below the water surface to enable a screw of a proper diameter 
to be got iu. 

572. Q. — But how does the matter stand in the case of ocean 
vessels ? 

A. — In the case of ocean vessels, it is found that paddle 
vessels fitted with the ordinary radial wheels, and screw vessels 
fitted with the ordinary screw, are about equally efl3.cient in calms 
and in fair or beam winds with light and medium immersions. 
If the vessels are loaded deeply, however, as vessels starting on a 
long voyage and carrying much coal must almost necessarily be, 
then the screw has an advantage, since the screw acts in its best 
manner when deeply immersed, and the paddles in their worst. 
When a screw and paddle vessel, however, of the same model and 
power are set to encounter head winds, the paddle vessel it is found 
has in all cases an advantage, not in speed, but in economy of fuel. 
For whereas in a paddle vessel, when her progress is resisted, the 
speed of the engine diminishes nearly in the proportion of the 
diminished speed of ship, it happens that in a screw vessel this 
is not so, — at least to an equal extent, — but the engines work 
with nearly the same rate of speed as if no increase of resistance 
had been encountered by the ship. It follows from this circum- 
stance, that whereas in paddle vessels the consumption of steam, 
and therefore of fuel, per hour is materially diminished when 
head winds occur, in screw vessels a similar diminution in the 
consumption of steam and fuel does not take place. 



SCREW AND PADDLE VESSEL TIED STERN TO STERN". 289 

573. Q. — But perhaps under such circumstances the speed 
of the screw vessel will be the greater of the two ? 

A, — No ; the speed of the two vessels will be the same, 
unless the strength of the head wind be so great as to bring the 
vessels nearly to a state of rest, and on that supposition the 
screw vessel will have the advantage. Such cases occur very 
rarely in practice ; and in the case of the ordinary resistances 
imposed by head winds, the speed of the screw and paddle 
vessel will be the same, but the screw vessel will consume most 
coals. 

574. Q, — What is th^ cause of this peculiarity ? 

A. — The cause is, that when the screw is so proportioned in 
its length as to be most suitable for propelling vessels in calms, 
it is too short to be suitable for propelling vessels which encoun- 
ter a very heavy resistance. It follows, therefore, that if it is 
prevented from pursuing its spiral course in the water, it will 
displace the water to a certam extent laterally, in the manner 
it does if the engine be set on when the vessel is at anchor ; and 
a part of the engine power is thus wasted in producing a use- 
less disturbance of the water, which in paddle vessels is not 
expended at all. 

575. Q. — If a screw and paddle vessel of the same mould 
and power be tied stern to stern, will not the screw vessel pre- 
ponderate and tow the paddle vessel astern against the whole 
force of her engines ? 

A. — Yes, that will be so. 

576. Q. — And seeing that the vessels are of the same mould 
and power, so that neither can derive an advantage from a 
variation in that condition, does not the preponderance of the 
screw vessel show that the screw must be the most powerful 
propeller ? 

A. — No, it does not. 

577. Q. — Seeing that the vessels are the same in all respects 
except as regards the propellers, and that one of them exhibits 
a superiority, does not this circumstance show that one pro- 
peller must be more powerful than the other ? 

A. — That does not follow necessarily, nor is it the fact in 



290 PREPONDERANCE OF SCREW VESSEL. 

this particular case. All steam vessels when set into motion, 
will force themselves forward with an amount of thrust which, 
setting aside the loss from friction and from other causes, will 
just balance the pressure on the pistons. In a paddle vessel, as 
has already been explained, it is easy to tell the tractive force 
exerted at the centre of pressure of the jDaddle wheels, when 
the pressure urging the pistons, the dimensions of the wheels 
and the speed of thp vessel are known ; and that force, what- 
ever be its amount, must always continue the same with any 
constant pressure on the pistons. In a screw vessel the same 
law applies, so that with any given pressure on the pistons and 
discarding the consideration of friction, it will follow that 
whatever be the thrust exerted by a paddle or a screw vessel, it 
must remain uniform whether the vessel is in motion or at rest, 
and whether moving at a high or a low velocity through the 
water. Now to achieve an equal speed during calms in two 
vessels of the same model, there must be the same amount of 
propelling thrust in each; and this thrust, whatever be its 
amount, cannot afterward vary if a uniform pressure of steam be 
maintained. The thrusts, therefore, caused by their respective 
propelling instruments, when a screw and paddle vessel are tied 
stern to stern, must be the same as at other times ; and as at 
other times those thrusts are equal, so must they be when the 
vessels are set in the antagonism supposed. 

578. Q,—How comes it then that the screw vessel pre- 
ponderates ? 

A. — Not by virtue of a larger thrust exerted by the screw in 
pressing forward the shaft and with it the vessel, but by the 
gravitation against the stern of the wave of water which the 
screw raises by its rapid rotation. This wave will only be 
raised very high when the progress of the vessel through the 
water is nearly arrested, at which time the centrifugal action 
of the screw is very great ; and the vessel under such circum- 
stances is forced forward partly by the thrust of the screw, and 
partly by the hydrostatic pressure of the protuberance of water 
which the centrifugal action of the screw raises up at the stern. 

579. Q. — Can you state any facts in corroboration of this view ? 



SCREW AND PADDLE VESSELS AT SEA. 291 

A. — The screw vessel will not prepnoderate if a screw and 
paddle vessel be tied bow to bow and the engines of each be 
then reversed. In some screw vessels the amount of thrust 
actually exerted by the screw under all its varying circum- 
stances, has been ascertained by the application of a dyna- 
mometer to the end of the shaft. By this instrument — which is 
formed by a combination of levers like a weighing machine for 
carts — a thrust or pressure of several tons can be measured by 
the application of a small weight; and it has been found, by 
repeated experiment with the dynamometer, that the thrust of 
the screw in a screw vessel when towing a paddle vessel against 
the whole force of her engines, is just the same as it is when the 
two vessels are maintaining an equal speed in calms. The pre- 
ponderance of the screw vessel must, therefore, be imputable to 
some other agency than to a superior thrust of the screw, which 
is found by experiment not to exist. 

580. Q, — Has the dynamometer been applied to paddle ves- 
sels? 

A. — It has not been applied to the vessels themselves, as in 
the case of screw vessels, but it has been employed on shore to 
ascertain the amount of tractive force that a paddle vessel can 
exert on a rope. 

581. Q. — Have any experiments been made to determine the 
comparative performances of screw and paddle vessels at sea ? 

A. — Yes, numerous experiments ; of which the best known 
are probably those made on the screw steamer Eattler and the 
paddle steamer Alecto, each vessel of the same model, size, and 
power, — each vessel being of about 800 tons burden and 200 
horses power. Subsequently another set of experiments with 
the same object was made with the Niger screw steamer and 
the Basilisk paddle steamer, both vessels being of about 1000 
tons burden and 400 horses power. The general results which 
were obtained in the course of these experiments are those 
which have been already recited. 

582. Q. — Will you recapitulate some of the main mcidents 
of these trials ? 

A. — I may first state some of the chief dimensions of the 



292 TIIIALS OF THE RATTLER AND ALECTO. 

vessels. The Eattler is 176 feet 6 inclies long, 32 feet 8 J inclies 
broad, 888 tons burden, 200 liorses j^ower, and lias an area of 
immersed midship section of 380 square feet at a draught of 
water of 11 feet 5^ inches. The Alecto is of the same dimen- 
sions in every respect, except that she is only of 800 tons bur- 
den, the difference in this particular being wholly owing to the 
Rattler having been drawn out about 15 feet at the stern, to 
leave abundant room for the application of the screw. The 
Eattler was fitted with a dynamometer, which enabled the 
actual propelling thrust of the screw shaft to be measured ; and 
the amount of this thrust, multiplied by the distance through 
which the vessel passed in a given time, would determine the 
amount of power actually utilized in propelling the ship. Both 
vessels were fitted with indicators applied to the cylinders, so as 
to determine the amount of power exerted by the engines. 

583. Q. — How many trials of the vessels were made on this 
occasion ? 

A. — Twelve trials in all ; but I need not refer to those in 
which similar or identical results were only repeated. The first 
trial was made under steam only, the weather was calm and the 
water smooth. At 54 minutes past 4 in the morning both vessels 
left the Nore, and at 30 J minutes past 2 the Rattler stopped her 
engines in Yarmouth Roads, where in 20^ minutes afterward she 
was joined by the Alecto. The mean speed achieved by the 
Rattler during this trial was 9*2 knots per hour; the mean 
speed of the Alecto was 8*8 knots per hour. The slip of the 
screw was 10*2 per cent. The actual power exerted by the 
engines, as shown by the indicator, was in the case of the 
Rattler 334*6 horses, and in the case of the Alecto 281*2 horses ; 
being a difference of 53*4 horses in favor of the Rattler. The 
forward thrust upon the screw shaft was 3 tons, 17 cwt., 3 qrs., 
and 14 lbs. The horse power of the shaft — or power actually 
utilized — ascertained by multiplying the thrust in pounds by the 
space passed through by the vessel in feet per minute, and 
dividing by 33,000, was 247*8 horses power. This makes the 
ratio of the shaft to the engine power as 1 to 1*3, or, in other 
words, it shows that the amount of engine power utilized in 



INDICATOR AND DYNAMOMETER POWEE. 293 

propulsion was 77 per cent. In a subsequent trial made with the 
vessels running before the wind, but with no sails set and the 
masts struck, the speed realized by the Rattler was 10 knots per 
hour. The slip of the screw was 11*3 per cent. The actual 
power exerted by the engines of the Rattler was 368-8 horses, 
The actual power exerted by the engines of the Alecto was 291*7 
horses. The thrust of the shaft was equal to a weight of 4 
tons, 4 cw^t., 1 qr., 1 lb. The horse power of the shaft was 290*2 
horses, and the ratio of the shaft to the engine power was 1 to 
1*2. Here, therefore, the amount of the engine power utilized 
was 84 per cent. 

584. Q. — ^If in any screw vessel the power of the engine be 
diminished by shutting off the steam or otherwise, you will then 
have a larger screw relatively with the power of the engine than 
before ? 

^.— Yes. 

585. §. — Was any experiment made to ascertain the effect 
of this modification ? 

A. — There was ; but the result was not found to be better 
than before. The experiment was made by shutting oft' the 
steam from the engines of the Rattler until the number of 
strokes was reduced to 17 in the minute. The actual power 
was then 126*7 horses ; thrust upon the shaft 2 tons, 2 cwt., 3 
qrs., 14 lbs ; horse power of shaft 88*4 horses ; ratio of shaft to 
engine power 1 to 1*4 ; slip of the screw' 18*7 per cent. In this 
experiment the power utilized was 71 per cent. 

586. §. — Was any experiment made to determine the rela- 
tive performances in head winds ? 

A. — The trial in which this relation was best determined 
lasted for seven hours, and was made against a strong head 
wind and heavy head sea. The speed of the Rattler by patent 
log was 4*2 knots ; and at the conclusion of the trial the Alecto 
had the advantage by about half a mile. Owing to an acci- 
dental injury to the indicator, the power exerted by the engines 
of the Rattler in this trial could not be ascertained ; but judg- 
ing from the power exerted in other experiments with the same 
number of revolutions, it appears probable that the power actu- 



294 KESISTAXCE PER SQUARE FOOT OF SECTION 

ally exerted by the Rattler was about 300 horses. The number 
of strokes per minute made by the engines of the Rattler was 
22, whereas in the Alecto the number of strokes per minute was 
only 12 ; so that while the engines of the Alecto were reduced, 
by the resistance occasioned by a strong head wind, to nearly 
half their usual speed, the engines of the Rattler were only 
lessened about one twelfth of their usual speed. The mean 
thrust upon the screw shaft during this experiment, was 4 tons, 
7 c^vt., qr., 16 lbs. The horse power of the shaft was 125*9 
horses, and the slip of the screw was 56 per cent. Taking the 
power actually exerted by the Rattler at 300 horses, the power 
utilized in this experiment is only 42 per cent. 

587. Q. — What are the dimensions of the screw in the 
Rattler ? 

A. — Diameter 10 feet, length 1 foot 3 inches, pitch 11 feet. 
The foregoing experiments show that with a larger screw a 
better average performance would be obtained. The best result 
arrived at, was when the vessel was somewhat assisted by the 
wind, which is equivalent to a reduction of the resistance of the 
hull, or to a smaller hull, which is only another expression for 
a larger proportionate screw. 

588. Q. — When you speak of a larger screw, what increase 
of dimension do you mean to express ? 

A. — ^An increase of the diameter. The amount of reacting 
power *of the screw upon the water is not measured by the 
number of square feet of surface of the arms, but by the area of 
the disc or circle in which the screw revolves. The diameter 
of the screw of the Rattler being 10 feet, the area of its disc is 
78"5 square feet ; and with the amount of thrust already men- 
tioned as existing in the first experiment, viz. 8722 lbs., the 
reacting pressure on each square foot of the screw's disc will be 
108^ lbs. The immersed midship section being 380 square feet, 
this is equivalent to 23 lbs. per square foot of immersed mid- 
ship section at a speed of 9*2 knots jDcr hour. 

589. Q. — In smaller vessels of similar form, will the resist- 
ance per square foot of midship section be more than this ? 

A, — It will be considerably more. In the Pelican, a vessel 



IS LARGEST IN SMALL VESSELS. 295 

of 109f square feet of midsliip section, I estimate the resistance 
per square foot of midship section at 30 lbs., when the speed of 
the vessel is 9*7 knots per hour. In the Minx with an immersed 
midship section of 82 square feet, the resistance per square foot 
of immersed midship section was found by the dynamometer to 
be 41 lbs. at a speed of 8^ knots ; and in the Dwarf, a vessel 
with 60 square feet of midship section, I estimate the resistance 
per square foot of midship section at 46 lbs. at a speed of 9 knots 
per hour, which is just double the resistance per square foot of 
the Eattler. The diameter of the screw of the Minx is 4^ feet, 
so that the area of its disc is 15*9 square feet, and the area of 
immersed midship section is about 5 times greater than that of 
the screw's disc. The diameter of the screw of the Dwarf is 5 
feet 8 inches, so that the area of its disc is 25*22 square feet, and 
the area of immersed midship section is 2*4 times greater than 
that of the screw's disc. The pressure per square foot of the 
screw's disc is 214 lbs. in the case of the Minx, and 109^ lbs. in 
the case of the Dwarf. 

590. Q, — From the greater jDroportionate resistance of smaH 
vessels, will not they require larger proportionate screws than 
large vessels ? 

^.— They will. 

591. Q. — Is there any ready means of predicting what the 
amount of thrust of a screw will be ? 

A, — When we know the amount of pressure on the pistons, 
and the velocity of their motion relatively with the velocity of 
advance made by the screw, supposing it to work in a solid nut, 
it is easy to tell what the thrust of the screw would be if it were 
cleared of the effects of friction and other irregular sources of 
disturbance. The thrust, in fact, would be at once found by 
the principle of virtual velocities ; and if we take this theoreti- 
cal thrust and diminish it by one fourth to compensate for fric- 
tion and lateral slip, we shall have a near approximation to the 
amount of thrust that will be actually exerted.* 

* See Treatise on the Screw Tropeller, by J. Bourne, C. E. 



296 BENEFITS OF A DEEPLY-IMMERSED SCREW. 



COMPARATIVE ADVANTAGES OF DIFFERENT SCREWS. 

592. Q, — What species of screw do you consider tlie best ? 
A, — In cases in which a large diameter of screw can be em- 

plo3^ed, the ordinary screw or helix with two blades seems to be 
as effective as any other, and it is the most easily constructed. 
If, however, the screw is restricted in diameter, or if the vessel 
is required to tow, or will have to encounter habitually strong 
head winds, it will be preferable to employ a screw with an in- 
creasing pitch, and also of such other configuration that it will 
recover from the water some portion of the power that has been 
expended in slip. 

593. Q. — How can this be done ? 

A. — There are screws which are intended to accomplish this 
object already in actual use. When there is much slip a centri- 
fugal velocity is given to the water, and the screw, indeed, if 
the engine be set on when the vessel is at rest, acts very much as 
a centrifugal fan would do if placed in the same situation. The 
water projected outward by the centrifugal force escapes in the 
line of least resistance, which is to the surface ; and if there be 
a high column of water over the screw, or, in other words, if the 
screw is deeply immersed, then the centrifugal action is resisted 
to a greater extent, and there will be less slip produced. The 
easiest expedient, therefore, for obviating loss by slip is to sink 
the screw deeply in the water ; but as there are obvious limits 
to the application of this remedy, the next best device is to 
recover and render available for propulsion some part of the 
power which has been expended in giving motion to the water. 
One device for doing this consists in placing the screw well for- 
ward in the dead wood, so that it shall be overhung by the 
stern of the ship. The water forced upward by the centrifugal 
action of the screw will, by impinging on the overhanging stem, 
press the vessel forward in the water, just in the same way as is 
done by the wind when acting on an oblique sail. I believe, 
the two revolving vanes without any twist or obliquity on them 
at all, would propel a vessel if set well forward in the dead 
wood or beneath the bottom, merely by the ascent of the water 



SCREWS WITH CONVERGENT ACTION. 297 

Up the inclined plane of the vessel's run ; and, at all events, a 
screw so placed would, in my judgment, aid materially in pro- 
pelling the vessel when her progress was resisted by head winds. 

594. Q. — But you said there are some kinds of screws which 
profess to accomplish this ? 

A. — There are screws which profess to counteract the centri- 
fugal velocity given to the water by imparting to it an equal 
centripetal force, the consequence of which will be, that the 
water projected backward by the screw, instead of taking the 
form of the frustum of a cone, with its small end next the 
screw, will take the form of a cylinder. One of these forms of 
screw is that patented by the Earl of Dundonald in 1843, and 
which is represented in j^^. 49. Another is the form of screw 
already represented in Jig. 48, and which was patented by 

Fig. 49. 



The Eakl of Dundonald's Propsller. 

Mr. Hodgson in 1844. Mr. Hodgson bends the arms of his pro- 
pellers backward, not into the form of a triangle, but into the 
form of a parabola, to the end that the impact of the screw on 
the particles of the water may cause them to converge to a 
focus, as the rays of light would do in a parabolic reflector. 
But this particular configuration is not important, seeing that 
the same convergence which is given to the particles of the 
water, with a screw of uniform pitch bent back into the form of 
a parabola, will be given with a screw bent back into the form 
of a triangle, if the pitch be suitably varied between the centre 
and the circumference. 



298 Griffith's and holm's sceews. 

595. Q, — Then the pitch may be varied in two ways ? 

A. — Yes : a screw may have a pitch increasing in the direc- 
tion of the length, as would happen in the case of a spiral 
stair, if every successive step in the ascent was thicker than the 
one below it ; or it may increase from the centre to the circum- 
ference, as would happen in the case of a spiral stair, if every step 
were thinner at the centre of the lower than at its outer wall. 
When the pitch of a screw increases in the direction of its length, 
the leading edge of the screw enters the water without shock 
or impact, as the advance of the leading edge per revolution 
will not be greater than the advance of the vessel. When the 
pitch of a screw increases in the direction of its diameter, the cen- 
tral part of the screw will advance with only the same velocity 
as the water, so that it cannot communicate any centrifugal velo- 
city to the water ; and the whole slip, as well as the whole pro- 
pelling pressure, will occur at the outer part of the screw blades. 

596. Q. — Is there any advantage derived from these forms 
of screws ? 

A. — There is a slight advantage, but it is so slight as hardly 
to balance the increased trouble of manufacture, and, conse- 
quently, they are not generally or widely adopted. 

597. Q. — What other kinds of screw are there i^roposing to 
themselves the same or similar objects ? 

A. — There is the corrugated screw, the arms of which are 
corrugated, so as it were to gear with the water during its revo- 
lution, and thereby prevent it from acquiring a centrifugal 
velocity. Then there is Griffith's screw, which has a large ball 
at its centre, which, by the suction it creates at its hinder part, 
in passing through the water, produces a converging force, 
which partly counteracts the divergent action of the arms. 
Finally, there is Holm's screw, which has now been applied to 
a good number of vessels with success. 

598. Q. — Will you describe the configuration and action of 
Holm's screw ? 

A. — First, then, the screw increases in the direction of its 
length, and this increase is very rapid at the following edge, so 
that, in fact, the following edge stands in the jDlane of the shaft, 



beattie's arrangement of the screw. 299 

or in the vertical longitudinal plane of tlie vessel. Then the 
ends of the arms are bent over into a curved flange, the edge of 
which points astern, and the point where this curved flange 
joins the following edge of the screw is formed, not into an 
angle, but into a portion of a sphere, so that this corner resem- 
bles the bowl of a spoon. When the screw is put into revolu- 
tion, the water is encountered by the leading edge of the screw 
without shock, as its advance is only equal to the advance of the 
vessel, and before the screw leaves the water it is projected 
directly astern. At the same time, the curved flange at the rim 
of the screw prevents the dispersion of the water in a radial 
direction, and it consequently assumes the form of a column or 
cylinder of water, projected backward from the ship. 

599. Q. — What is the nature of Beattie's- screw ? 

A. — Beattie's screw is an arrangement of the screw propeller 
whereby it is projected beyond the rudder, and the main object 
of the arrangement is to take away the vibratory motion at the 
stern, — an intention which it accomplishes in practice. There 
is an oval eye in the rudder, to permit the screw shaft to pass 
through it. 

600. Q, — When the diameter of the cylinder of water pro- 
jected backward by a screw, and the force urging it into motion 
are known, may not the velocity it will acquire be approxi- 
mately determined ? 

A, — That will not be very difllcult ; and I will take for illus- 
tration the case of the Minx, already referred to, which will 
show how such a computation is to be conducted. The speed 
of this vessel, in one of the experiments made with her, was 
8*445 knots ; the number of revolutions of the screw per min- 
ute, 231*32 ; and the pressure on each square foot of area of the 
screw's disc, 214 lbs. If a knot be taken to be 6075-6 feet, then 
the distance advanced by the vessel, when the speed is 8*445 
knots, will be 3*7 feet per revolution, and this advance will be 
made in about -26 of a second of time. Now the distance which 
a body will fall by gravity, in -26 of a second, is 1*087 feet ; 
and a weight of 214 lbs. put into motion by gravity, or by a 
pressure of 214 lbs., would, therefore, acquire a velocity of 



300 SCREW SHIPS SHOULD HAVE SHARP STERNS. 

1-087 feet during the time one revolution of the screw is being 
performed. The weight to be moved, however, is 3*7 cubic feet 
of water, that being the new water seized by the screw each 
revolution for every square foot of surface in the screw's disc ; 
and 3*7 cubic feet of water weigh 231*5 lbs., so that the urging 
force of 214 lbs. is somewhat less than the force of gravity, and 
the velocity of r^otion communicated to the water will be some- 
what under 1*087 feet per revolution, or we may say it will be 
in round numbers 1 foot per revolution. This, added to the 
progress of the vessel, will make the distance advanced by the 
screw through the water 4*7 feet per revolution, leaving the 
difference between this and the pitch, namely 1*13 feet, to be 
accounted for on the supposition that the screw blades had 
broken laterally through the water to that extent. It would be 
proper to apply some correction to this computation, which 
would represent the increased resistance due to the immersion of 
the screw in the water ; for a column of water cannot be moved in 
the direction of its axis beneath the surface, without giving mo- 
tion to the superincumbent water, and the inertia of this super- 
incumbent water must, therefore, be taken into the account. In 
the experiment upon the Minx, the depth of this superincum- 
bent column was but small. The total amount of the slip was 
36*53 per cent. ; and there will not be much error in setting 
down about one half of this as due to the recession of the water 
in the direction of ther vessel's track, and the other half as due 
to the lateral penetration of the screw blades. 

601. Q. — Is it not important to make the stern of screw ves- 
sels very fine, with the view of diminishing the slip, and in- 
creasing the speed ? 

A. — It is most important. The Rifleman, a vessel of 486 
tons, had originally engines of 200 horses power, which pro- 
pelled her at a speed of 8 knots an hour. The Teazer, a vessel 
of 296 tons, had originally engines of 100 horses power, which 
propelled her at a speed of 6^ knots an hour. The engines of 
the Teazer were subsequently transferred to the Rifleman, and 
new engines of 40 horse power were put into the Teazer. Both 
vessels were simultaneously sharpened at the stern, and the 



PEOPER PROPORTIONS OF SCREWS. 301 

result was, that the 100 horse engines drove the Rifleman, when 
sharpened, as fast as she had previously been driven by the 200 
horse engines; and the 40 horse engines drove the Teazer, 
when sharpened, a knot an hour faster than she had previously 
been driven by the 100 horse engines. The immersion of both 
vessels was kept unchanged in each case ; and the 100 horse 
engines of the Teazer, when transferred to the Rifleman, drove 
that vessel, after she had been sharpened, 2 knots an hour faster 
than they had previously driven a vessel not much more than 
half the size. These are important facts for every one to be 
acquainted with who is interested in the success of screw ves- 
sels, and who seeks to obtain the maximum of efficiency with 
the minimum of expense.* 

PROPORTIONS OF SCREWS. 

602. Q. — In fixing upon the proportions of a screw proper to 
propel any given vessel, how would you proceed ? 

A, — I would first compute the probable resistance of the 
vessel, and I would be able to find the relative resistances of the 
screw and hull, and in every case it is advisable to make the 
screw as large in diameter as possible. The larger the screw is, 
the greater will be the efficiency of the engine in propelling the 
vessel ; the larger will be the ratio of the pitch to the diameter, 
which produces a maximum efiect ; and the smaller will be the 
length of the screw or the fraction of a convolution to produce 
a maximum efiect. 

603. Q, — Will you illustrate this doctrine by a practical 
example ? 

-4. — The French screw steamer Pelican was fitted succes- 
sively with two screws of four blades, but the diameter of the 
first screw was 98-42 inches, and the diameter of the second 54 
inches. If the efficiency of the first screw by represented by 1, 
that of the second screw will be represented by '823, or, in other 
words, if the first screw would give a speed of 10 knots, the 
second would give little more than 8. The most advantageous 

* See Treatise on the Screw Propeller, by John Bourne, C. E. 
14 



302 DEDUCTIONS OF MM. BOURGOIS AND MOLL. 

ratio of pitch to diameter was found to be 2*2 in the case of the 
large screw, and 1*384 in the case of the small. The fraction 
of a convolution which was found to be most advantageous was 
•281 in the case of the large screw, and -^SO in the case of the 
small screw. 

604. Q. — Were screws of four blades found to be more 
efficient than screws with two ? 

A, — They were found to have less slip, but not to be more 
efficient, the increased slip in those of two blades being balanced 
by the increased friction in those of four. Screws of two blades, 
to secure a maximum efficiency, must have a finer pitch than 
screws of four. 

605. Q. — Are the proportions found to be most suitable in 
the case of the Pelican applicable to the screws of other ves- 
sels? 

A. — Only to those which have the same relative resistance 
of screw and hull. Taking the relative resistance to be the area 
of immersed midship section, divided by the square of the 
screw's diameter, it will in the case of the Rattler be Jf ^ or 3-8. 
From the experiments made by MJM. Bourgois and Moll on the 
screw steamer Pelican, they have deduced the proportions of 
screws proper for all other classes of vessels, whether the screws 
are of two, four, or six blades. 

606. §.— Will you specify the nature of their deductions ? 
A, — I will first enumerate those which bear upon screws 

with two blades. When the relative resistance is 5*5 the ratio 
of pitch to diameter should be 1'006, and the fraction of the 
pitch or proportion of one entire convolution should be 0*454. 
When the relative resistance is 5, the ratio of pitch to diameter 
should be 1*069, and fraction of pitch 0*428 ; relative resistance 
4'5, pitch 1*135, fraction 0*402 ; relative resistance 4, pitch 
1*205, fraction 0*378 ; relative resistance 3*5, pitch 1*279, frac- 
tion 0*355 ; relative resistance 3, pitch 1*357, fraction 0*334 ; 
relative resistance 2*5, pitch 1*450, fraction 0*313 ; relative re- 
sistance 2, pitch 1*560, fraction 0*294 ; relative resistance 1*5, 
pitch 1*682, fraction 0*275. The relative resistance of 4 is that 
which is usual in an auxiiiary line of battle ship, 3*5 in an 



CONJOINT ACTION OF STEAM AND SAILS. 303 

auxiliary frigate, 3 in a high speed line of battle ship, 2*5 in a 
high speed frigate, 2 in a high speed corvette, and 1*5 in a 
high speed despatch boat. 

607. Q, — What are the corresponding proportions of screws 
of four blades ? 

A. — The ratios of the pitches to the diameter being for each 
of the relative resistances enumerated above, 1*342, 1*425, 1*513, 
1*607, 1*705, 1*810, 1*933, 2*080, and 2*243, the respective frac- 
tions of pitch or fractions of a whole convolution will be 0*455, 
0*428, 0*402, 0*378, 0*355, 0334, 0*313, 0*294, and 0*275. 

608. Q. — And what are the corresponding proportions 
proper for screws of six blades ? 

A. — Beginning with the relative resistance of 5*5 as before, 
the proper ratio of pitch to diameter for that and each of the 
successive resistances in the case of screws with six blades, will 
be 1*677, 1*771, 1*891, 1*2009, 2*131, 2*262, 2*416, 2*600, 2*804 ; 
and the respective fractions of pitch will be 0*794, 0*749, 0*703, 
0*661, 0*621, 0*585, 0*548, 0*515, and 0*481. These are the pro- 
portions which will give a maximum performance in every 
case.* 

SCREW VESSELS WITH FULL AND AUXILIARY POWER. 

609. Q, — Do you consider that the screw propeller is best 
adapted for vessels of full power, or for vessels with auxiliary 
power ? 

A, — It is, in my opinion, best adapted for vessels with 
auxiliary power, and it is a worse propeller than paddle wheels 
for vessels which have habitually to encounter strong head 
winds. Screw vessels are but ill calculated — at least as con- 
structed heretofore — ^to encounter head winds, and the legiti- 
mate sphere of the screw is in propelling vessels with auxiliary 
power. 

610. Q, — Does the screw act well in conjunction with sails ? 
A, — I cannot say it acts better than paddles, except in so far 

In my Treatise on the Screw Propeller I have gone into these various ques- 
tions more fully than would consort with the limits of this publication. 



304 EXPENSE OF TRANSPORT IN DIFFERENT VESSELS. 

as it is less in tlie way and is less affected by tlie listing or heel- 
ing over of the ship. A small steam power, however, acts very 
advantageously in aid of sails, for not only does the operation 
of the sails in reducing the resistance of the hull virtually in- 
crease the screw's diameter, but the screw, by reducing the 
resistance which has to be overcome by the sails and by increas- 
ing the speed of the vessel, enables the sails to act with greater 
efiiciency, as the wind will not rebound from them with as great 
a velocity as it would otherwise do, and a larger proportion of 
the power of the wind will also be used up. In the case of 
beam winds, moreover, the action of the screw, by the larger 
advance it gives to the vessel will enable the sails to intercept a 
larger column of wind in a given time. It appears, therefore, 
that the sails add to the efficiency of the screw, and that the 
screw also adds to the efficiency of the sails. 

611. Q. — What is the comparative cost of transporting mer- 
chandise in paddle steamers of full power, in screw steamers of 
auxiliary power, and in sailing ships ? 

A, — That will depend very much upon the locality where 
the comparison is made. In the case of vessels performing dis- 
tant ocean voyages, in which they may reckon upon the aid of 
uniform and constant winds, such as the trade winds or the 
monsoon, sailing ships of large size will be able to carry more 
cheaply than any other species of vessel. But where the winds 
are irregular and there is not much sea room, or for such cir- 
cumstances as exist in the Channel or Mediterranean trades, 
screw vessels with auxiliary power will constitute the cheapest 
instrument of conveyance. 

612. Q. — Are there any facts recorded illustrative of the 
accuracy of this conclusion ? 

A. — A full paddle vessel of 1000 tons burden and 350 horses 
power, will carry about 400 tons of cargo, besides coal for a 
voyage of 500 miles, and the expense of such a voyage, includ- 
ing wear and tear, depreciation, &c., will be about 190?. The- 
duration of the voyage will be about 45| hours. A screw ves- 
sel of 400 tons burden and 100 horses power, will carry the same 
amount of cargo, besides her coals, on the same voyage, and 



CONJOINT ACTION OF SCREW AND PADDLES. 305 

the expense of the voyage, including wear and tear, deprecia- 
tion, &c., will be not much more than 60Z. An auxiliary screw 
vessel, therefore, can carry merchandise at one third of the cost 
of a full-powered paddle vessel. By similar comparisons made 
bety/een the expense of conveying merchandise in auxiliary 
screw steamers and sailing ships on coasting voyages, it appears 
that the cost in screw steamers is about one third less than in 
the sailing ships ; the greater expedition of the screw steamers 
much more than compensating for the expense which the main- 
tenance of the machinery involves. 

SCEEW AND PADDLES COMBINED. 

613. Q. — Would not a screw combined with paddles act in 
a similarly advantageous way as a screw or paddles when aided 
by the wind ? 

A. — ^If in any given paddle vessel a supplementary screw be 
added to increase her power and speed, the screw will act in a 
more beneficial manner than if it had the whole vessel to pro- 
pel itself, and for a like reason the paddles will act in a more 
beneficial manner. There will be less slip both upon the pad- 
dles and upon the screw than if either had been employed 
alone ; but the same object would be attained by giving the 
vessel larger paddles or a larger screw. 

614. Q. — Have any vessels been constructed with combined 
screw and paddles ? 

A. — Not any that I know of, except the great vessel built 
under the direction of Mr. Brunei. The Bee many years since 
was fitted with both screw and paddles, but this was for the 
purpose of ascertaining the relative efficiency of the two modes 
of propulsion, and not for the purpose of using both together. 

615. Q, — What would be the best means of accelerating the 
speed of a paddle vessel by the introduction of a supplementary 
screw ? 

A. — If the vessel requires new boilers, the best course of 
procedure would be to work a single engine giving motion to 
the screw with high pressure steam, and to let the waste steam 



30G BENEFITS OF ACCELERATING TADDLE WHEELS 

from the liigli pressure engine work the paddle engines. In 
this way the power might be doubled without any increased 
expenditure of fuel per hour, and there would be a diminished 
expenditure per voyage in the proportion of the increased speed. 

616. <2. — What would the increased speed be by doubling 
the power ? 

A, — The increase would be in the proportion of the cube 
root of 1 to the cube root of 2, or it would be 1*25 times 
greater. If, therefore, the existing speed were 10 miles, it 
would be increased to 12^ miles by doubling the power, and 
the vessel would ply with about a fourth less coals by increas- 
ing the power in the manner suggested. 

617. Q, — Is not high pressure steam dangerous in steam 
vessels ? 

A, — Not necessarily so, and it has now been introduced into 
a good number of steam vessels with satisfactory results. In 
the case of locomotive engines, where it is used so widely, very 
few accidents have occurred ; and in steam vessels the only 
additional source of danger is the salting of the boiler. This 
may be prevented either by the use of fresh water in the boiler, 
or by practising a larger amount of blowing off, to insure which 
it should be impossible to diminish the amount of water sent 
into the boiler by the feed pump, and the excess should be dis- 
charged overboard through a valve near the water level of the 
boiler, which valve is governed by a float that will rise or fall 
with the fluctuating level of the water. If the float be a copper 
ball, a little water should be introduced into it before it is 
soldered or brazed up, which will insure an equality of pressure 
within and without the ball, and a leakage of water into it will 
then be less likely to take place. A stone float, however, is 
cheaper, and if properly balanced will be equally effective. All 
steam vessels should have a large excess of boiling feed water 
constantly flowing into the boiler, and a large quantity of water 
constantly blowing off through the surface valves, which being 
governed by floats will open and let the superfluous water 
escape whenever the water level rises too high. In this way the 
boiler will be kept from salting, and priming will be much less 



BY AN AUXILIARY SCREW AT THE STERN. _ 307 

likely to occur. The great problem of steam navigation is the 
economy of fuel, since the quantity of fuel consumed by a vessel 
will very much determine whether she is profitable or otherwise. 
Notwithstanding the momentous nature of this condition, how- 
ever, the consumption of fuel in steam vessels is a point to 
which very little attention has been paid, and no efficient means 
have yet been adopted in steam vessels to insure that measure 
of economy which is known to be attainable, and which has 
been attained already in other departments of engineering in 
Which the benefits of such economy are of less weighty import. 
It needs nothing more than the establishment of an efficient sys- 
tem of registration in steam vessels, to insure a large and rapid 
economy in the consumption of fuel, as this quality would then 
become the test of an engineer's proficiency, and would deter- 
mine the measure of his fame. In the case of the Cornish 
engines, a saving of more than half the fuel was speedily effected 
by the introduction of the simple expedient of registration. In 
agricultural engines a like economy has speedily followed from 
a like arrangement ; yet in both of these cases the benefits of a 
large saving are less eminent than they would be in the case of 
steam navigation ; and it is to be hoped that this expedient of 
improvement will now be speedily adopted. 



CHAPTER X. 

EXAMPLES OF ENGINES. 



OSCILLATING PADDLE ENGINES. 

618. Q. — Will you describe the structure of an oscillating 
engine as made by Messrs. Penn ? 

A. — To do this it will be expedient to take an engine of a 
given power, and then the sizes may be given as well as an 
account of the configuration of the parts : we may take for an 
example a pair of engines of 21^ inches diameter of cylinder, 
and 22 inches stroke, rated by Messrs. Penn at 12 horses power 
each. The cylinders of this oscillating engine are placed beneath 
the cranks, and, as in all Messrs. Penn's smaller engines, the 
piston rod is connected to the crank pin by means of a brass 
cap, provided with a socket, by means of which it is cuttered 
to the piston rod. There is but one air pump, which is situated 
within the condenser between the cylinders, and it is wrought 
by means of a crank in the intermediate shaft — this crank 
being cut out of a solid piece of metal as in the formation of 
the cranked axles of locomotive engines. The steam enters the 
cylinder through the outer trunnions, or the trunnions adjacent 
to the ship's sides, and enters the condenser through the two 
midship trunnions — a short three ported valve being placed 
on the front of the cylinder to regulate the flow of steam to 



penn's oscillating paddle engine. 309 

and from tlie cylinder in the proper manner. The weight of 
this valve on one side of the cylinder is balanced by a weight 
hung upon the other side of the cylinder; but in the most 
recent engines this weight is discarded, and two valves are 
used, which balance one another. The framing consists of an 
upper and lower frame of cast iron, bound together by eight 
malleable iron colunms : upon the lower frame the pillow blocks 
rest which carry the cylinder trunnions, and the condenser and 
the bottom frame are cast in the same piece. The upper frame 
supports the paddle shaft pillow blocks ; and pieces are bolted 
on in continuation of the upper frame to carry the paddle 
wheels, which are overhung from the journal. 

619. Q, — What are the dimensions and arrangement of the 
framing ? 

A. — The web, or base plate of the lower frame is f of an 
inch thick, and a cooming is carried all round the cylinder, 
leaving an opening of sufficient size to permit the necessary 
oscillation. The cross section of the upper frame is that of a 
hollow beam 6 inches deep, and about 3| inches wide, with 
holes at the sides to take out the core ; and the thickness of the 
metal is ff ths of an inch. Both the upper and the lower frame 
is cast in a single piece, with the exception of the continuations 
of the upper frame, which support the paddle wheels. An 
oval ring 3 inches wide is formed in the upper frame, of suffi- 
cient size to permit the working of the air pump crank ; and 
from this ring feathers run to the ends of the cross portions of 
the frame which supports the intermediate shaft journals. The 
columns are 1| inches in diameter ; they are provided with 
collars at the lower ends, which rest upon bosses in the lower 
frame, and with collars at the upper ends for supporting the 
upper frame ; but the upper collars of two of the corner columns 
are screwed on, so as to enable the columns to be drawn up 
when it is lequired to get the cylinders out. The cross section 
of the bottom frame is also of the form of a hollow beam, 7 inches 
deep, except in the region of the condenser, where it is, of course, 
of a different form. The depth of the boss for the reception of the 
columns is a little more than 7 inches deep on the lower frame, 



310 pexn's oscillating paddle engine. 

and a little more than 6 inches deep on the upper frame ; and the 
holes through them are so cored out, that the columns only bear 
at the upper and lower edges of the hole, instead of all through 
it — a formation by which the fitting of the columns is facilitated. 

620. Q. — What are the dimensions of the condenser ? 

A. — The condenser, which is cast upon the lower frame, 
consists of an oval vessel 22^ inches wide, by 2 feet 4J inches 
long, and 1 foot lOJ inches deep ; it stands 9 inches above the 
upper face of the bottom frame, the rest projecting beneath it ; 
and it is enlarged at the sides by being carried beneath the 
trunnions. 

621. Q. — What are the dimensions of the air pump ? 

A, — The air pump, which is set in the centre of the conden- 
ser, is 15 J inches in diameter, and has a stroke of 11 inches. 
The foot valve is situated in the bottom of the air pump, and 
its seat consists of a disc of brass, in which there is a rectan- 
gular flap valve, opening upwards, but rounded on one side to 
the circle of the pump, and so balanced as to enable the valve 
to open with facility. The balance weight, which is formed of 
brass cast in the same piece as the valve itself, operates as a stop, 
by coming into contact with the disc which constitutes the 
bottom of the pump ; the disc being recessed opposite to the 
stop to enable the valve to open sufficiently. This disc is bolted 
to the barrel of the pump by means of an internal flange, and 
before it can be removed the ]3ump must be lifted out of its 
place. The air pump barrel is of brass to which is bolted a cast 
iron mouth piece, with a port for carrying the water to the hot 
well ; within the hot well the delivery valve, which consists of 
a common flap valve, is situated. The mouth piece and the air 
pump barrel are made tight to the condenser, and to one another, 
by means of metallic joints carefully scraped to a true surface, 
so that a little white or red lead interposed makes an air tight 
joint. The air pump bucket is of brass, and the valve of the 
bucket is of the common pot lid or spindle kind. The injection 
water enters through a single cock in front of the condenser — 
the jet striking against the barrel of the air pump. The air 
pump rod is maintained in its vertical position by means of 



PEOPOKTIONS OF THE CYLINDER. 311 

guides, the lower ends of wliicli are bolted to the mouth of the 
13ump, and the upper to the oval in the top frame, within which 
the air pump crank works ; and the motion is communicated 
from this crank to the pump rod by means of a short connected 
rod. The lower frame is not set immediately below the top 
frame, but 2| inches behind it, and the air pump and condenser 
are 2| inches nearer one edge of the lower frame than the other. 

622. Q. — What are the dimensions of the cylinder ? 

A, — The thickness of the metal of the cylinder is,-^^ths of an 
inch ; the depth of the belt of the cylinder is 9^ inches, and its 
greatest projection from the cylinder is 2~ inches. The distance 
from the lower edge of the belt to the bottom of the cylinder 
is 11 1 inches, and from the upper edge of the belt to the top 
flange of the cylinder is 9 inches. The trunnions are 7J inches 
diameter in the bearings, and 3| inches in width ; and the 
flanges to which the glands are attached for screwing in the 
trimnion packings are 1^ inch thick, and have ]ths of an inch 
of projection. The width of the packing space round the 
trunnions is |ths of an inch, and the diameter of the pipe 
passing through the trunnion 4|ths, which leaves fjths for the 
thickness of the metal of the bearing. Above and below each 
trunnion a feather runs from the edge of the belt or bracket 
between 3 and 4 inches along the cylinder, for the sake of 
additional support ; and in large engines the feather is con- 
tinued through the interior of the belt, and cruciform feathers 
are added for the sake of greater stiffness. The projection of 
the outer face of the trunnion flange from the side of the cylin- 
der is 6 J inches ; the thickness of the flange round the mouth 
of the cylinder is f of an inch, and its projection 1| inch ; the 
height of the cylinder stuffing box above the cylinder cover is 
4 J inches, and its external diameter 4| inches — the diameter of 
the piston rod being 2^ inches. The thickness of the stuffing 
box flange is 1| inch. 

623. Q. — Will you describe the nature of the communication 
between the cylinder and condenser ? 

A, — The pipe leading to the condenser from the cylinder is 
made somewhat bell mouthed where it joins the condenser, and 



312 penn's oscillating paddle engine. 

tlie gland for compressing tlie packing is made of a larger 
internal diameter in every part except at the point at wluch the 
X3ipe emerges from it, where it accurately fits the pipe so as to 
enable the gland to squeeze the packing. By this construction 
the gland may be drawn back without being jammed upon the 
enlarged part of the pipe ; and the enlargement of the pipe 
toward the condenser prevents the air pump barrel from offering 
any impediment to the free egress of the steam. The gland is 
made altogether in four pieces : the ring which presses the 
packing is made distinct from the flange to which the bolts are 
attached which force the gland against the packing, and both 
ring and flange are made in two pieces, to enable them to be 
got over the pipe. The ring is half checked in the direction 
of its depth, and is introduced without any other support to 
keep the halves together, than what is afforded by the interior 
of the stuffing box ; and the flange is half checked in the direc- 
tion of its thickness, so that the bolts which press down the ring 
by passing through this half-checked part, also keep the segments 
of the flange together. The bottom of the trunnion packing 
space is contracted to the diameter of the eduction pipe, so as to 
prevent the packing from being squeezed into the jacket ; but the 
eduction pipe does not fit quite tight into this contracted part, 
but, while in close contact on the lower side, has about ^g^d 
of an inch of space between the top of the pipe and the cylin- 
der, so as to permit the trunnions to wear to that extent without 
throwing a strain upon the pipe. The eduction pipe is attached 
to the condenser by a flange joint, and the bolt holes are all 
made somewhat oblong in the perpendicular direction, so as to 
permit the pipe to be slightly lowered, should such an opera- 
tion be rendered necessary by the wear of the trunnion bear- 
ings; but in practice the wear of the trunnion bearings is 
found to be so small as to be almost inappreciable. 

624. Q. — Will you describe the valve and valve casing ? 
A. — The length of the valve casing is 16^ inches, and its pro- 
jection from the cylinder is 3| inches at the top, 4J inches at 
the centre, and 2^ inches at the bottom, so that the back of the 
valve casing is not made flat, but is formed in a curve. The 



penn's oscillating paddle engine. 313 

width of the valve casing is 9 inches, but there is a portion of 
the depth of the belt 1| inch wider, to permit the steam to 
enter from the belt into the casing. The valve casing is at- 
tached to the cylinder by a metallic joint ; the width of the 
flange of this joint is IJ inch, the thickness of the flange on the 
casing I inch, and the thickness of the flange on the cylinder 
I ths of an inch. The projection from the cylinder of the passage 
for carrying the steam upwards, and downwards, from the valve 
to the top and bottom of the cylinder, is 2J inches, and its 
width externally 8f inches. The valve is of the ordinary three 
ported description, and both cylinder and valve faces are of 
cast iron. 

625. Q. — What description of piston is used ? 

A. — The piston is packed with hemp, but the junk ring is 
made of malleable iron, as cast iron junk rings have been found 
liable to break : there are four plugs screwed into the cylinder 
cover, which, when removed, permit a box key to be introduced, 
to screw down the piston packing. The screws in the junk ring 
are each provided with a small ratchet, cut in a washer fixed 
upon the head, to prevent the screw from turning back ; and 
the number of clicks given by these ratchets, in tightening up 
the bolts, enables the engineer to know when they have all been 
tightened equally. In more recent engines, and especially in 
those of large size, Messrs. Penn employ for the piston packing 
a single metallic ring with tongue piece and indented 
plate behind the joint ; and this ring is packed behind with 
hemp squeezed by the junk ring as in ordinary hemp-packed 
pistons. 

626. Q. — "Will you describe the construction of the cap for 
connecting the piston rod with the crank pin ? 

A. — The cap for attaching the piston rod to the crank pin, 
is formed altogether of brass, which brass serves to form the 
bearing of the crank pin. The external diameter of the socket 
by which this cap is attached to the piston rod is 3 ^^g inches. 
The diameter of the crank pin is 3 inches, and the length of 
the crank pin bearing 3 J inches. The thickness of the brass 
around the crank pin bearing is 1 inch, and the upper portion 



314 pexn's oscillating paddle engine. 

of the brass is secured to the lower portion by means of lugs, 
which are of such a depth that the perpendicular section 
through the centre of the bearing has a square outline measur- 
ing 7 inches in the horizontal direction, 3| inches from the 
centre of the pin to the level of the top of the lugs, and 2| 
inches from the centre of the pin to the level of the bottom 
of the lugs. The width of the lugs is 2 inches, and the bolts 
passing through them are IJ inch in diameter. The bolts are 
tapped into the lower portion of the cap, and are fitted very 
accurately by scraping where they pass through the upper por- 
tion, so as to act as steady pins in preventing the cover of the 
crank pin bearing from' being worked sideways by the alternate 
thrust on each side. The distance between the centres of the 
bolts is 5 inches, and in the centre of the cover, where the lugs, 
continued in the form of a web, meet one another, an oil 
cup If inch in diameter, IJ inch high, and provided with an 
internal pipe, is cast upon the cover, to contain oil for the lubri- 
cation of the crank pin bearing. The depth of the cutter for 
attaching the cap to the piston rod is IJ inch and its thickness 
is |ths of an inch. 

627. Q. — Will you describe the means by which the air 
pump rod is connected with the crank which works the air 
pump ? 

A. — A similar cap to that of the piston rod attaches the air 
pump crank to the connecting rod by which the air pump rod 
is moved, but in this instance the diameter of the bearing is 5 
inches, and the length of the bearing is about 3 inches. The air 
pump connecting rod and cross head are shown in perspective 
inj^^. 50. The thickness of the brass encircling the bearing of 
the shaft is three fourths of an inch upon the edge, and 1 \ inch 
in the centre, the back being slightly rounded ; the width of the 
lugs is If inch, and the depth of the lugs is 2 inches upon the 
upper brass, and 2 inches upon the lower brass, making a total 
depth of 4 inches. The diameter of the bolts passing through the 
lugs is 1 inch, and the bolts are tapped into the lower brass, and 
accurately fitted into the upper one, so as to act as steady pins, 
as in the previous instance. The lower eye of the connecting 



CONNECTIONS OF THE AIR PUMP. 



315 



rou IS forked, so as to admit the eye of the air pump rod ; and 
the pin which connects the two together is prolonged into a 
cross head, as shown in fig, 50. The ends of this cross head 
move in guides. The forked end of the connecting rod is fixed 

Fig. 50. 




Air Pump Connecting Eod and Cross Head. Messrs. Pcnn. 



upon the cross head by means of a feather, so that the cross head 
partakes of the motion of the connecting rod, and a cap, similar 
to that attached to the piston rod, is attached to the air pump 
rod, for connecting it with the cross head. The diameter of the 
air pump rod is 1^ inch, the external diameter of the socket 
encircling the rod is 2 J inches, and the depth of the socket 4| 
inches from the centre of the cross head. The d^pth of the cutter 



316 tenn's oscillating paddle engine. 

for attaching the socket to the rod is 1 inch, and its thickness -^ 
inch. The breadth of the lugs is If inch, the depth IJ inch, 
making a total depth of 2^ inches ; and the diameter of the 
bolts seven eighths of an inch. The diameter of the cross head 
at the centre is 2 inches, the thickness of each jaw around the 
bearing 1 inch, and the breadth of each ^^ inch. 

628. Q. — What are the dimensions of the crank shaft and 
cranks ? 

A. — The diameter of the intermediate shaft journal is 4,-^5- 
inches, and of the paddle shaft journal 4f inches ; the length of 
the journal in each case is 5 inches. The diameter of the large 
eye of the crank is 7 inches, and the diameter of the hole 
through it is 4f inches ; the diameter of the small eye of the 
crank is oj inches, the diameter of the hole through it being 3 
inches. The depth of the large eye is 4| inches, and of the 
small eye 3| inches ; the breadth of the web is 4 inches at the 
shaft end, and 3 inches at the pin end, and the thickness of the 
web is 2| inches. The width of the notch forming the crank 
in the intermediate shaft for working the air pump is 3 J inches, 
and the width of each of the arms of this crank is 3y| inches. 
Both the outer and inner corners of the crank are chamfered 
away, until the square part of the crank meets the round of the 
shaft. The method of securing the cranks pins into the crank 
eyes of the intermediate shaft consists in the application of a nut 
to the end of each pin, where it passes through the eye, the 
projecting end of the pin being formed with a thread upon 
which the nut is screwed. 

629. Q. — Will you describe the eccentric and eccentric rod ? 
A, — The eccentric and eccentric rod are shown in Jig, 51 

The eccentric is put on the crank shaft in two halves, joined 
in the diameter of largest eccentricity by means of a single bolt 
passing through lugs on the central eye, and the back balance 
is made in a separate piece five eighths of an inch thick, and is 
attached by means of two bolts, which also help to bind the 
halves of the eccentric together. The eccentric strap is half an 
inch thick, and IJ inch broad, and the flanges of the eccentric, 
within which the strap works, are each three eighths of an inch 



CONSTRUCTION OF THE ECCENTRIC. 



317 



thick. The eccentric rod is attached to the eccentric hoop by- 
means of two bolts passing through lugs upon the rod, and 
tapped into a square boss 
upon the hoop; and pieces 
of iron, of a greater or less 
thickness, are interposed be- 
tween the surfaces in setting 
the valve, to make the ec- 
centric rod of the right 
length. The eccentric rod 
is kept in gear by the push 
of a small horizontal rod, 
attached to a vertical blade 
spring, and it is thrown out 
of gear by means of the ordi- 
nary disengaging apparatus, 
which acts in opposition to 
the spring, as, in cases where 
the eccentric rod is not ver- 
tical, it acts in opposition to 
the gravity of the rod. 

630. §.— Will you explain 
in detail the construction of 
the valve gearing, or such 
parts of it as are peculiar to 
the oscillating engine ? 

A. — The eccentric rod is 
attached by a pin, 1 inch in 
diameter, to an open curved 
link or sector with a tail 
projecting upward and pass- 
ing through an eye to guide 
the link in a vertical mo- 
tion. The link is formed 
of iron case-hardened, and 
is 2 1 inches deep at the 
middle, and 2| inches deep at the ends, and 1 inch broad. 




Eccentric and Rod. Messrs. Penn. 



318 penn's oscillating paddle engine. 

The opening in the link, which extends nearly its entire length, 
is lj%- inch broad ; and into this opening a brass block 2 inches 
long is truly fitted, there being a hole through the block f inch 
diameter, for the reception of the pin of the valve shaft lever. 
The valve shaft is If inch diameter at the end next the luik or 
segment, and diminishes regularly to the other end, but its 
cross section assumes the form of an octagon in its passage 
round the cylinder, measuring mid-way IJ inch deep, by about 
f inch thick, and the greatest depth of the finger for moving 
the valve is about 1 inch. The depth of the lever for moving 
the valve shaft is 2 inches at the broad, and 1^ inch at the 
narrow end. The internal breadth of the mortice in which the 
valve finger moves is y% inch, and its external depth is If inch, 
which leaves three eighths of an inch as the thickness of metal 
round the hole ; and the breadth, measuring in the direction 
of the hole, is 1 ^ inch. The valve rod is three fourths of an 
inch in diameter, and the' mortice is connected to the valve rod 
by a socket 1 inch long, and 1| inch diameter, through which 
a small cutter passes. A continuation of the rod, eleven six- 
teenths of an inch diameter, passes upward from the mortice, 
and works through an eye, which serves the purpose of a guide. 
In addition to the guide afforded to the segment by the ascend- 
ing tail, it is guided at the ends upon the colunms of the fram- 
ing by means of thin semicircular brasses, 4 inches deep, pass- 
ing round the columns, and attached to the segment by two | inch 
bolts at each end, passing through projecting feathers upon the 
brasses and segment, three eighths of an inch in thickness. The 
curvature of the segment is such as to correspond with the arc 
swept from the centre of the trunnion to the centre of the valve 
lever pin -^hen the valve is at half stroke as a radius ; and the 
operation of the segment is to prevent the valve from being 
affected by the oscillation of the cylinder, but the same action 
would be obtained by the employment of a smaller eccentric 
with more lead. In some engines the segment is not formed in 
a single piece, but of two curved blades, with blocks interposed 
at the ends, which may be filed do^Ti a little, to enable the 
sides of the slot to be brought nearer, as the metal wears away. 



PLUMMER BLOCKS OF SHAFTS AND TRUNNIONS. 319 

631. Q. — What kind of plummer blocks are used for the 
paddle shaft bearmgs ? 

A, — The paddle shaft plummer blocks are altogether of 
brass, and are formed in much the same manner as the cap of 
the piston rod, only that the sole is flat, as in ordinary plummer 
blocks, and is fitted between projecting lugs of the framing, to 
prevent side motion. In the bearings fitted on this plan, how- 
ever, the upper brass will generally acquire a good deal of play 
after some amount of wear. The bolts are worked slack in the 
holes, though accurately fitted at first ; and it appears expedient, 
therefore, either to make the bolts very large, and the sockets 
through which they pass very deep, or to let one brass fit into 
the other. 

632. §.— How are the trunnion plummer blocks made ? 

A, — The trunnion plummer blocks are formed in the same 
manner as the crank shaft plummer blocks ; the nuts are kept 
from turning back by means of a pinching screw passing through 
a stationary washer. It is not expedient to cast the trunnion 
plummer blocks upon the lower frame, as is sometimes done ; 
for the cylinders, being pressed from the steam trunnions by the 
steam, and drawn in the direction of the condenser by the 
vacuum, have a continual tendency to approach one another ; 
and as they wear slightly toward midships, there would be no 
power of readjustment unless the plummer blocks were mov- 
able. The flanges of the trunnions should always fit tight 
against the plummer block sides, but there should be a little 
play sideways at the necks of the trunnions, so that the cylinder 
may be enabled to expand when heated, without throwing an 
undue strain upon the trunnion supports. 

633. Q, — What kind of paddle wheel is supplied with these 
oscillating engines ? 

• A. — ^The wheels are of the feathering kind, 9 feet 8 inches in 
diameter, measuring to the edges of the floats ; and there are 10 
floats upon each wheel, measuring 4 feet 6 inches long each, and 
18^ inches broad. There are two sets of arms to the wheel, 
which converge to a cast iron centre, formed like a short pipe 
with large flanges, to which the arms are affixed. The diameter 



320 penn's oscillating paddle engine. 

of the shaft, where the centre is put on, is 4 J inches, the exter- 
nal diameter of the pipe is 8 inches, and the diameter of the 
flanges is 20 inches, and their thickness 1| inch. The flanges 
are 12 inches asunder at the outer edge, and they partake of 
the converging direction of the arms. The arms are 2| inches 
broad, and half an inch thick ; the heads are made conical, and 
each is secured into a recess upon the side of the flange by 
means of three bolts. The ring which connects together the 
arms, runs round at a distance of 3 feet 6 inches from the centre, 
and the projecting ends of the arms are bent backward the length 
of the lever which moves the floats, and are made very wide 
and strong at the point where they cross the ring, to which they 
are attached by four rivets. The feathering action of the floats 
is accomplished by means of a pin fixed to the interior of the 
paddle box, set 3 inches in advance of the centre of the shaft, 
and in the same horizontal line. This pin is encircled by a 
cast iron collar, to which rods are attached 1 1 inch diameter in 
the centre, proceeding to the levers, 7 inches long, fixed on the 
back of the floats in the line of the outer arms. One of these 
rods, however, is formed of nearly the same dimensions as one 
of the arms of the wheel, and is called the driving arm, as it 
causes the cast iron collar to turn round with the revolution of 
the wheel, and this collar, by means of its attachments to the 
floats, accomplishes the feathering action. The eccentricity in 
this wheel is not sufficient to keep the floats in the vertical posi- 
tion, but in the position between the vertical and the radial. 
The diameter of the pins upon which the floats turn is 1 ^ inch, 
and between the pins and paddle ring two stud rods are set 
between each of the projecting ends of the arms, so as to pre- 
vent the two sets of arms from being forced nearer or further 
apart ; and thus prevent the ends of the arms from hindering 
the action of the floats, by being accidentally jammed upon the 
sides of the joints. Stays, crossing one another, proceed from 
the inner flange of the centre to the outer ring of the wheel, and 
from the outer flange of the centre to the inner ruig of the wheel^ 
with the view of obtaining greater stiflhess. The floats are 
formed of plate iron, and the whole of the joints and joint pina 



VAEIOTJS OSCILLATING PADDLE ENGINES. 321 

are steeled, or formed of steel. For sea-going vessels the most 
approved practice is to make the joint pins of brass, and also to 
bush the eyes of the joints with brass ; and the surface should 
be large to diminish wear. 

634. Q. — Can you give the dimenions of any other oscilla- 
ting engines ? 

A, — In Messrs. Penn's 50 horse power oscillating^ engine, the 
diameter of the cylinder is 3 feet 4 inches, and the length of the 
stroke 3 feet. The thickness of the metal of the cylinder is 1 
inch, and the thickness of the cylinder bottom is If inch, 
crossed with feathers, to give it additional stifeess. The 
diameter of the trunnion bearings is 1 foot 2 inches, and the 
breadth of the trunnion bearings 5| inches. Messrs. Penn, 
in their larger engines, generally make the area of the steam 
trunnion less than that of the eduction trunnion, in the pro- 
portion of 32 to 37 ; and the diameter of the eduction trunnion 
is regulated by the internal diameter of the eduction pipe, 
which is about Jth of the diameter of the cylinder. But a 
somewhat larger proportion than this appears to be expedient : 
Messrs. Kennie make the area of their eduction pipes, in oscilla- 
ting engines, -^-^^ of the area of the cylinder. In the oscilla- 
ting engines of the Oberon, by Messrs. Rennie, the cylinder is 
61 inches diameter, and 1^ inch thick above and below the 
belt, but in the wake of the belt it is 1] inch thick, which is 
also the thickness of metal of the belt itself. The internal depth 
of the belt is 2 feet 6 inches, and its internal breadth is 4 
inches. The piston rod is 6| inches in diameter, and the total 
depth of the cylinder stuffing box is 2 feet 4 inches, of which 18 
inches consists of a brass bush — this depth of bearing being em- 
ployed to prevent the stuffing box or cylinder from wearing oval. 

635. Q. — Can you give any other examples ? 

A. — The diameter of cylinder of the oscillating engines of 
the steamers Pottinger, Ripon, and Indus, by Miller & Raven- 
hill, is 76 inches, and the length of the stroke 7 feet. The 
thickness of the metal of the cylinder is IJ-^ inch ; diameter of 
the piston rod 8i inches ; total depth of cylinder stuffing box 
3 feet ; depth of bush in stuffing box 4 inches ; the rest of tho 



322 VARIOUS DETAILS OF OSCILLATING ENGINES. 

depth, with the exception of the space for packing, being occu- 
pied with a very deep gland, bushed with brass. The internal 
diameter of the steam pipe is 13 inches ; diameter of steam 
truDnion journal 25 inches ; diameter of eduction trunnion jour- 
nal 25 inches ; thickness of metal of trunnions 2^ inches ; length 
of trunnion bearings 11 inches ; projection of cylinder jacket, 
8 inches; depth of packing space in trunnions, 10 inches; 
width of packing space in trunnions, or space round the 
pipes, IJ inch ; diameter of crank pin 10| inches ; length of 
bearing of crank pin 15^ inches. There are six boilers on the 
tubular plan in each of these vessels ; the length of each boiler 
is 10 feet 6 inches, and the breadth 8 feet; and each boiler 
contains 62 tubes 3 inches in diameter, and 6 feet 6 inches 
long, and two furnaces 6 feet 4| inches long, and 3 feet IJ 
inch broad. 

636. Q. — Is it the invariable practice to make the piston rod 
cap of brass in the way you have described ? 

A. — In all oscillating engines of any considerable size, the 
cover of the connecting brass, which attaches the crank pin to 
the connecting rod, is formed of malleable iron ; and the socket 
also, which is cuttered to the end of the piston rod, is of malle- 
able iron, and is formed w^ith a T head, through which bolts 
pass up through the brass, to keep the cover of the brass in 
its place. 

637. Q, — Is the piston of an oscillating engine made deeper 
than in common engines ? 

A. — It is expedient, in oscillating engines, to form the piston 
with a projecting rim round the edge above and below, and a 
corresponding recess in the cylinder cover and cylinder bottom, 
whereby the breadth of bearing of the solid part of the metal 
will be increased, and in many engines this is now done. 

638. Q. — Would any difficulty be experienced in keeping the 
trunnions tight in a high pressure oscillating engine ? 

A. — It is very doubtful whether the steam trunnions of a 
high pressure oscillating engine will continue long tight 
if the packing consists of hemp ; and it appears preferable 
to introduce a brass ring, to embrace the pipe, cut spirally, 



323 

with an overlap piece to cover the cut, and packed behind 
with hemp. 

639. Q. — How is the packing of the trunnions usually 
effected ? 

A. — The packing of the trunnions, after being plaited as 
hard as possible, and cut to the length to form one turn round 
the pipe, is dipped into boiling tallow, and is then compressed 
in a mould, consisting of two concentric cylinders, with a gland 
forced down into the annular space by three to six screws in the 
case of large diameters, and one central screw in the case of 
small diameters. Unless the trunnion packings be well com- 
pressed, they will be likely to leak air, and it is, therefore, 
necessary to pay particular attention to this condition. It is 
also very important that the trunnions be accurately fitted into 
their brasses by scraping, so that there may not be the smallest 
amount of play left upon them ; for if any upward motion is 
permitted, it will be impossible to prevent the trunnion pack- 
ings from leaking. 

DIEECT ACTING SCEEW ENGINE. 

640. Q. — Will you describe the configuration and construc- 
tion of a direct acting screw engine ? 

A. — I will take as an example of this species of engine, 
the engine constructed by Messrs. John Bourne & Co., for the 
screw steamer Alma, a vessel of 500 tons burden. This engine 
is a single steeple engine laid on its side, and in its general 
features it resembles the engines of the Amphion already 
described, only that there is one cylinder instead of two. The 
cylinder is of 42 inches diameter and 42 inches stroke, and the 
vessel has been propelled by this single engine at the rate of 
fourteen miles an hour. 

641. Q. — ^Is not a single engine liable to stick upon the 
centre so that it cannot be started or reversed with facility ? 

A. — A single engine is no doubt more liable to stick upon 
the centre than two engines, the cranks of which are set at 
right angles with one another; but numerous paddle vessels 



324 bouene's direct acting sceew engine. 

are plying successfully that are propelled by a single engine, 
and the screw offers still greater facility than paddles for such a 
mode of construction. In the screw engine referred to, as the 
cylinder is laid upon its side, there is no unbalanced weight to 
be lifted up every stroke, and the crank, whereby the screw 
shaft is turned round, consists of two discs with a heavy side 
intended to balance the momentum of the piston and its con- 
nections; but these counter-weights by their gravitation also 
prevent the connecting rod and crank from continuing in the 
same line when the engine is stopped, and in fact they place the 
crank in the most advantageous position for starting again 
when it has to be set on. 

642. Q. — Will you explain the general aiTangement of the 
parts of this engine ? 

A. — The cylinder lies on its side near one side of the vessel, 
and from the end of the cylinder two piston rods extend to a cross 
head sliding athwartships, in guides, near the other side of the 
vessel. To this cross head the connecting rod is attached, and 
one end of it partakes of the motion of the cross head or piston, 
while the other end is free to follow the revolution of the crank 
on the screw shaft. 

643. Q. — What is the advantage of two discs entering into 
the composition of the crank instead of one ? 

A. — A double crank, such as two discs form with the crank 
pin, is a much steadier combination than would result if only 
one disc were employed with an over-hung pin. Then the 
friction on the neck of the shaft is made one half less by being 
divided between the two bearings, and the short prolongation 
of the shaft beyond the journal is convenient for the attachment 
of the eccentrics to work the valves. 

644. Q. — Will you enumerate some of the principal dimen- 
sions of this engine ? 

A, — The bottom frame, on which also the condenser is cast, 
forms the base of the engine : on one end of it the cylinder is 
set ; on the other end are the guides for the cross head, and in 
the middle are the bearings for the crank shaft. The part 
where the cylinder stands is two feet high above the engine 



THE BOTTOM FRAME AND CYLINDER. 325 

platform, and the elevation to the centre of the guides or the 
centre of the shaft is 10 inches higher than this. The metal 
both of the side frames and bottom flange is 1{ inch thick. 
The cylinder has flanges cast on its sides, upon which it rests on 
the bottom frame, and it is sunk between the sides of the frame 
so as to bring the centre of the cylinder in the same plane as the 
centre of the screw shaft. The opening left at the guides for 
the reception of the guide blocks is 6 inches deep, and the 
breadth of the bearing surface is 11 inches. The cover of the 
guides is 8 inches deep at the middle, and about half the depth 
at the ends, and holes are cored through the central web for 
two oil cups on each guide. The brass for each of the crank 
shaft bearings is cut into four pieces so that it may be tighten- 
ed in the up and down direction by the bolts, which secure 
the plummer block cap, and tightened in the athwartship direc- 
tion, which is the direction of the strain, by screwing up a 
wedge-formed plate against the side of the brass, a parallel 
plate being applied to the other side of the brass, which may be 
withdrawn to get out the wedge piece when the shaft requires 
to be lifted out of its place. The air pump is bolted to one side 
of the bottom frame, and a passage is cast on it conducting 
from the condenser to the air pump. In this passage the inlet 
and outlet valves at each end of the air pump are situated, and 
appropriate doors are formed above them to make them easily 
accessible. The outlet passage leading from the air pump 
communicates with the waste water pipe, through which the 
water expelled by the air pump is discharged overboard. 

645. Q.—ls the cylinder of the usual strength and configura- 
tion? 

A. — The cylinder is formed of cast iron in the usual way, 
and is 1 J inch thick in the barrel. The ends are of the same 
thickness, but are each stiffened with six strong feathers. The 
piston is cast open. The bottom of it is |ths of an inch thick, 
and it is stiffened by six feathers f of an inch thick ; but the 
feather connecting the piston rod eyes is 1 J inch thick, and the 
metal round the eyes is 2 inches thick. The piston is closed by 
a disc or cover |ths of an inch thick, secured by 15 bolts, and 
16 



326 bouene''s direct acting screw engine. 

tliis cover answers also the purpose of a junk ring. The piston 
23acking consists of a single cast iron ring 3^ inches broad, and 
I inch thick, packed behind with hemp. This ring is formed 
with a tongue piece, with an indented plate behind the cut ; 
and the cut is oblique to prevent a ridge forming in the cylin- 
der. The total thickness of the piston is 5 J inches. The piston 
rods are formed with conical ends for fitting into the piston, but 
are coned the reverse way as in locomotives, and are secured in 
the piston by nuts on the ends of the rods, these nuts being pro- 
vided with ratchets to prevent them from unscrewing acci- 
dentally. 

646. Q, — What species of slide valve is employed ? 

A. — The ordinary three ported valve, and it is set on the top 
of the cylinder. The cylinder ports are 4^ inches broad by 24 
inches long ; and to relieve the valve from the great friction due 
to the pressure on so large a surface, a balance piston is placed 
over the back of the valve, to which it is connected by a strong 
link ; and the upward pressure on this piston being nearly the 
same as the downward pressure on the valve, it follows that the 
friction is extinguished, and the valve can be moved with great 
ease with one hand. The balance piston is 21 inches in diame- 
ter. In the original construction of this balance piston two 
faults were committed. The passage communicating between 
the condenser and the top of the balance piston was too small, 
and the pins at the ends of the link connecting the valve and 
balance piston were formed with an inadequate amount of 
bearmg surface. It followed from this misproportion that the 
balance piston, being adjusted to take off nearly the whole of the 
pressure, lifted the valve off the face at the beginning of each 
stroke. For the escape of the steam into the eduction passage 
momentarily impaired the vacuum subsisting there, and owing 
to the smallness of the passage leading to the space above the 
balance piston, the vacuum subsisting in that space could 
not be impaired with equal rapidity. The balance piston, 
therefore, rose by the upward pressure upon it momentarily 
predominating over the downward pressure on the valve ; but 
this fault was corrected by enlarging the communicating pas- 



CONNECTING ROD AND CEOSS HEAD. 



327 



sage between the top of the balance piston and the eduction 
pipe. The smallness of the pins at the ends of the link con- 
necting the valve and balance piston, caused the surfaces to cut 
into one another, and to wear very rapidly, and the pins and 
eyes in this situation should be large in diameter, and as long as 
they can be got, as they are not so easily lubricated as the other 
bearings about the engine, and are moreover kept at a high tem- 
perature by the steam. The balance piston is packed in the same 
way as the main piston of the engine. Its cylinder, which is only 
a few inches in length, is set on the top of the valve casing, and 
a trunk projects upwards from its centre to enable the connect- 
ing link to rise up in it to attain the necessary length. 

647. Q. — What is the diameter of the piston 
rods and connecting rod ? 

A. — The piston rods, which are two in num- 
ber, are 3 inches diameter, and 12 feet 10 inches 
long over all. They were, however, found to be 
rather small, and have since been made- half an 
inch thicker. The connecting rod consists of 
two rods, wliich are prolongations of the bolts 
that connect the sides of the brass bushes which 
encircle the crank pin and cross head. The con- 
necting rod is shown in perspective in fig. 53. 
The rods composing it are each 2J inches in 
diameter. 

648. Q. — ^Will you describe the configuration 
of the cross head. 

A, — The cross head, exhibited in fig. 53, is 
a round piece of iron like a short shaft, with 
two unequal arms keyed upon it, the longer of 
which & works the air pump, and the shorter c 
works the feed pump. The piston rods enter 
these arms at a a. The cross head is 8 inches 
rliameter where it is embraced by the connecting 
rod at 6, and 7 inches diameter where the air pump 
and feed pump arms are fixed on. The ends of the cross head 
dd^ for a length of 12 inches, are reduced to 3 inches diameter 



CoNNECTINO R 'O. 

Messrs. Bourne c*t Q». 



328 bourne's direct acting screw engine. 

where they fit into round holes in the centre of the guide 
blocks. Those blocks are of cast iron 6 inches deep, 11 inches 
wide, and 14 inches long, and they are formed with flanges 1 

Fig. 53. 




C 
Cross IIead and Pump Arms. Messrs. Bourne & Co. 

inch thick on the inner sides of the blocks. The projection of 
the air pump lever from the centre of the cross head is 1 foot 9 
inches, and it is bent 5 J inches to one side to enable it to engage 
the air pump rod. The eye of this arm is 6 inches broad and 
about 2 inches thick. At the part wherje one of the piston rods 
passes through it, the arm is 8 inches deep and 6 inches wide ; but 
the width thereafter narrows to 3 inches, and finally to 2 inches ; 
and the depth of the web of the arm reduces from 8 inches at 
the piston rod, to 4 inches at the eye, which receives the end 
of the air pump rod. The feed pump arm is only 3 inches 
thick, and has 9 inches of projection from the centre of the 
cross head ; but the eye attached to it on the opposite side of 
the cross head for the reception of the other piston rod is of 
the same length as that part of the air pump arm which one of 
the piston rods passes through. The j)iston rods have strong nuts 
on each side of each of these arms to attach them to the arms, 
and also to enable the length of the piston rods to be suitably 
adjusted, to leave equal clearance between the piston and eacli 
end of the cylinder at the termination of the stroke. 

649. Q. — Will you recapitulate the main particulars of the 
air pump ? 

A, — The air pump is made of brass 12^ inches diameter and 



AIR PUMP, CRANK, AND CRANK PIN. 329 

42 inches stroke, and tlie metal of the barrel is ,%ths of an inch 
thick. The air pump bucket is a solid piston of brass, 6^ inches 
deep at the edge, and 7 inches deep at the eye ; and in the edge 
three grooves are turned to hold water which answers the pur- 
pose of packing. The inlet and outlet valves of the air pump 
consist of brass plates 4 inch with strong feathers across them, 
and in each plate there are six grated perforations covered by 
India rubber discs 7 inches in diameter. These six perforations 
afford collectively an area for the passage of the water equal 
to the area of the pump. The air pump rod is of brass, 3| inches 
diameter. 

650. Q. — What are the constructive peculiarities of the 
discs and crank pin ? 

A, — The discs, which are 64 inches diameter, are formed of 
cast iron, and are 2^ inches thick in the body, and 5 inches 
broad at the rim. The crank shaft is 8 J inches diameter, and 
the central boss of the disc which receives the shaft measures 
10 inches through the eye, and the metal of the eye is 3 inches 
thick. In the part of the disc opposite to the crank pin, the 
web is thickened to 10 inches for nearly the whole semicircle, 
with the view of making that side of the disc heavier than the 
other side ; and when the engine is stopped, the gravitation of 
this heavy side raises the crank pin to the highest point it can 
attain, whereby it is placed in mid stroke, and cannot rest 
with the piston rods and connecting rod in a horizontal line. 
The crank pin is 8| inches diameter, and the length of the 
bearing or rubbing part of it is 16 inches. It is secured at the 
ends to the discs by flanges 18 inches diameter, and 2 inches 
thick. These flanges are indented into thickened parts of the 
discs, and are each attached to its corresponding disc by six 
bolts 2 inches diameter, countersunk in the back of the disc, 
and tapped into the malleable iron flange. Besides this attach- 
ment, each end of the pin, reduced to 4^ inches diameter, passes 
through a hole in its corresponding disc, and the ends of the 
pin are then riveted over. The crank pin is perforated through 
the centre by a small hole about I of an inch in diameter, and 
three perforations proceed from this central hole to the surface 






BOURNE'S DIRECT ACTING SCREW ENGINE. 



of the pin. Each crank shaft bearing is similarly perforated, 
and pipes are cast in the discs connecting these perforations 
together. The result of this arrangement is, that a large part 
of the oil or water fed into the bearings of the shaft is driven 
by the centrifugal action of the discs to the surface of the crank 
pin, and in this way the crank pin may be oiled or cooled with 
water in a very effectual manner. To intercept the water or oil 
which the discs thus drive out by their centrifugal action, a light 
paddle box or splash board of thin sheet brass is made to cover 
the upper part of each of the discs, and an oil cup with depend- 
ing wick is supported by the tops of these paddle boxes, which 
wick is touched at each revolution of the crank by a bridge 
standing in the middle of an oil cup attached to the crank pin. 
The oil is wiped from the wick by the projecting bridge at 

Fig. 54. 




Double Disc Crank. Messrs. Bourne & Co. 



each revolution, and subsides into the cup from whence it pro- 
ceeds to lubricate the crank pin bearing. This is the expedient 
commonly employed to oil the crank pins of direct acting 



EXPEDIENTS OF LUBRICATION^. 



331 



engines ; but in the engine now described, there are over and 
above this expedient, the communicating passages from the 
shaft bearings to the surface of the pin, by which means any 
amount of cooling or lubrication can be administered to the 
crank pin bearing, without the necessity of stopping or slowing 
the engine. 

651. Q. — What is the diam^eter of the screw shaft ? 

A. — The screw shaft is 7^ inches diameter, but the bearings 
on each side of the disc are 8^ inches diameter, and 16 inches 
long. Between the side of the disc and the side of the con- 
tiguous bearings there is a short neck extending 4| inches in 
the length of the shaft, and hollowed out somewhat to permit 
the passage of the piston rod ; for one piston rod passes imme- 
diately above the shaft on the one side of the discs, and the 
other piston rod passes immediately below the shaft on the 
other side of the discs. A short piece of one piston rod is 
shown in^^. 54. 

653. Q. — How is the thrust of the screw shaft received ? 

A. — The thrust of the screw shaft is received upon 7 collars, 
each 1 inch thick, and with 1 inch of projection above the 
shaft. The plummer block for receiving the thrust of the shaft 
is shown in fig. 55, and the coupling to enable the screw pro- 



ng. 55. 




Thrust BEAKiNa. 
Messrs. Bourne «fe Co. 



Coupling Ceanks. 
Messrs. Bourne & Co. 



peller to be disconnected from the engine, so that it may revolve 
freely when the vessel is under sail, is shown in fig, 56. When 



332 bourne's direct acting screw engine. 

it is required to disengage the propeller from the engine, the pins 
passing through the opposite eyes shown uifig. 56, are withdrawn 
by means of screws provided for that purpose, and the propeller 
and the engine are thenceforth independent of one another. 

653. Q. — Will you describe the arrangement of the valve 
gearing ? 

A. — The end of the screw shaft, after emerging from the 
bearing beside the disc, is reduced to a diameter of 4 inches, 
and is prolonged for 4 J- inches to give attachment to the cam 
or curved plate which gives motion to the expansion valve. 
This plate is 3| inches thick, and a stud 3^ inches diameter is 
fixed in the plate at a distance of 5 inches from the centre of 
the shaft. To this stud an arm is attached which extends to a 
distance of 2 inches from the centre of the shaft in the opposite 
direction, and the end of this arm carries a pin of 2^ inches diam- 
eter. From the pin most remote from the centre of the shaft, a 
rod 2^ inches broad and 1 inch thick extends to the upper end 
^. ^^ of the link of the link motion ; and from 

Fig. 57. . ' 

the pm least remote from the centre of the 
shaft, a similar rod extends to the lower 
end of the link of the link motion. This 
link, which is represented in fg. 57, is 2J 
inches broad, 1 inch thick, and is capable 
of being raised or lowered 25 inches in all. 
In the open part of the link is a brass 
block, which, by raising or lowering the link, 
takes either the position in which it is rep- 
resented at the centre of the link, or a posi- 
tion at either end of it. Through the hole 
in the brass block a pin passes to attach 
Link MotioxV. the brass to the end of a lever fixed on 

Messrs. Bourne & Co. ^^^ ^^^^^ ^^^^^^ . ^^ ^^^^^ whatever motion 

is imparted to the brass block is communicated to the valve 
through the medium of this lever. If the brass block be set in 
the middle of the link, no motion is communicated to it, and 
the valve being consequently kept stationary and covering 
both ports, the engine stops. If the link be lowered until the 




SPEED OF ENGINE VOO FEET PER MINUTE. 333 

brass block comes to the upper end of the link, the valve 
receives the motion of the eccentric for going ahead, and 
the engine moves ahead ; whereas if the link be raised until the 
brass block comes to the lower end of the link, the valve receives 
the motion of the backing eccentric, and the engine moves 
astern. Instead of eccentrics, however, pins at the end of the 
shaft are employed in this engine, the arrangement partaking 
of the nature of a double crank ; but the backing pin has less 
throw than the going ahead pin, whereby the efficient length of 
the link for going ahead is increased ; and the operation of back- 
ing, which does not require to be performed at the highest rate 
of speed, is sufficiently accommodated by about half the throw 
being given to the valve that is given in going ahead. A valve 
shaft extends across the end of the cylinder with two levers 
standing up, which engage horizontal side rods extending jfrom a 
small cross head on the end of the valve rod. A lever extends 
downwards from the end of the valve shaft, which is connected 
by a pin to the brass block within the link ; and the link is 
moved up or down by the starting handle, which, by means of 
a spring bolt shooting into a quadrant, holds the starting handle 
at any position in which it may be set. 

654. Q. — What is the diameter and pitch of the screw 
propeller ? 

A. — The diameter is 7 feet and the pitch 14 feet. The 
propeller is Holm's conchoidal propeller. Its diameter is 
smaller than is advisable, being limited by the draught of 
water of the vessel; and the vessel was required to have a 
small draught of water to go over a bar. This engine makes, 
under favorable circumstances, 100 strokes per minute. The 
speed of piston with this number of strokes is 700 feet per minute, 
and the engine works steadily at this speed, the shock and tre- 
mor arising from the arrested momentum of the moving parts 
being taken away by the counterbalance applied at the discs. 

LOCOMOTIVE ENGINE. 

655. Q. — Will you describe the principal features of a 
modern locomotive engine ? 



334 gooch's locomotive engine. 

A. — I will take for this purpose tlie locomotive Snake, con- 
structed by John.y. Gooch for the London and South Western 
Kailway, as an example of a modem locomotive of good con- 
struction, adapted for the narrow gauge. The length of the 
wheel base of this engine is 12 feet 8^ inches. There are two 
cylinders, each 14} inches diameter and 21 inches stroke. The 
total weight of the engine is 19 tons ; and this weight is so 
distributed on the wheels as to throw 8 tons on the leading 
wheels, 6 tons on the driving wheels, and 5 tons on the hind 
wheels. The engine is made with outside cylinders, and 
the cylinders are raised somewhat out of the horizontal line to 
enable them better to clear the leading wheels. 

656. Q. — What are the dimensions of the boiler ? 

A. — The interior of the fire box is 3 feet K^ inches wide by 3 
feet 5^ inches long, measuring in the direction of the rails. The 
area of the fire grate is consequently 12.4 square feet. The 
bars are somewhat lower on the side next the fire door than at 
the side next the tubes, and the mean height of the crown of the 
fire box above the bars is 3 feet 10 inches. The top edge of the 
fire door is about 7 inches lower than the crown of the fire box. 
The fire box is divided transversely by a corrugated feather or 
bridge of plate iron, containing water, about 31 inches wide, 
and of about one-third of the height of the fire box in the 
centre of the feather, and about two-thirds the height of the 
fire box at the sides where it joins the sides o.f the fire box. 
The internal shell of the fire box tapers somewhat upwards to 
facilitate the disengagement of the steam. It is about 2 inches 
narrower and shorter at the top than at the bottom ; the water 
space between the external and internal shell of the fire box 
being 2 inches at the bottom and 3 inches at the top. 

657. Q. — Of what material is the fire box composed ? 

A. — The external shell of the fire box is formed of iron 
X)lates ^ths of an inch thick, and the internal shell is formed of 
copper plates I inch thick, but the tube plate is J inch thick. 
The fire grate is rectangular, and the internal and external 
shells are tied together by iron stay bolts J inch diameter, and 
pitched about 4 inches apart. The roof of the fire box is stiffened 



r 



FRAMEWORK OF THE BOILER. 335 

by six strong bars extending from side to side of the fire box 
like beams, and the top of the fire box is secured to these bars, 
so that it cannot be forced down without breaking or bending 
them. 

658. Q. — What are the dimensions of the barrel of the 
boiler ? 

A. — The barrel of the boiler is 3 feet 7| inches in diameter, 
and 10 feet long. It is formed of iron plates |ths of an inch 
thick, riveted together. It is furnished with 181 brass tubes 
1^ inch diameter and 10 feet long, secured at the ends by ferules. 
The tube plate at the smoke box end is |ths of an inch thick, 
and the tube plates above the tubes are tied together by eight 
iron rods ^ths of an inch thick, extending from end to end of the 
boiler. The metal of the tubes is somewhat thicker at the end 
next the fire, being 13 wire gauge at fire box end, and 14 wire 
gauge at smoke box end. The rivets of the boiler are f inch 
diameter and 1^ inch pitch. The plating of the ash pan is y^ths 
of an inch thick, and the plating of the smoke box is f^ths of 
an inch thick. 

659. Q. — Will you describe the structure of the framework 
on which the boiler and its attachments rest, and in which 
the wheels are set ? 

A. — The framework or framing consists of a rectangular 
structure of plate iron circumscribing the boiler, with projecting 
lugs or arms for the reception of the axles of the wheels. In 
this engine the sides of the rectangle are double, or, as far as 
regards the sides, there are virtually two framings, one for the 
reception of the driving axles, and the other for the reception 
of the axles not connected with the engine. The whole of the 
parts of the outer and inner framings are connected together by 
knees at the comers, and the double sides are elsewhere con- 
nected by intervening brackets and stays, so as to constitute 
the whole into one rigid structure. The whole of the plat- 
ing of the inside frame is J inch thick and 9 inches deep. 
The plating of the outside frame is of the same thickness and 
depth at the fore part, until it reaches abaft the position of the 
cylinders and guides, where it reduces to ^ inch thick. The 



336 gooch's locomotive engine. 

axle guard of the leading wheels is formed of f plate bolted to 
the frame with angle iron guides. The axle guards of the trail- 
ing wheels are formed of two | inch plates, with cast iron blocks 
between them to serve as guides. The ends of the rectangular 
frame are formed of plates f thick, and at the front end there is 
a buffer beam of oak 4^ inches thick and 15 inches deep. The 
draw bolt is 2 inches diameter. There are two strong stays on 
each side, joining the barrel of the boiler to the inside framing, 
and one angle iron on each side joining the bottom of the smoke 
box to the inside framing. 

660. Q. — Of what construction are the wheels ? 

A. — The wheels and axles are of wrought iron, and the tires 
of the wheels are of steel. The driving wheels are 6 feet 6^ 
inches in diameter, and the diameter of crank pin is 3i inches. 
The diameter of the smaller wheels is 48^ inches. The axle 
boxes are of cast iron with bushes of Fenton's metal, and the 
leading axle has four bearings. The springs are formed of steel 
plates, 3 feet long, 4 inches broad, and -J inch thick. The axle 
of the driving wheel has two eccentrics, forged solid upon it, for 
working the pumps. 

661. Q. — Will you specify the dimensions of the principal 
parts of the engine ? 

A. — Each of the cylinders which is 14^ inches diameter, has 
the valve casing cast upon it. The steam ports are 13 inches 
long and 1| inches broad, and the exhaust port is 2^- inches 
broad. The travel of the valve is 4| inches, the lap 1 inch, and 
the lead | inch. The piston is 4 inches thick : its body is 
formed of brass with a cover of cast iron, and between the body 
and the cover two flanges, forged on the piston rod, are intro- 
duced to communicate the push and pull of the piston to the 
rod. The piston rod is of iron, 2 J inches diameter. The guide 
bars for guiding the top of the piston rod are of steel, 4 inches 
broad, fixed to rib iron bearers, with hard wood I of an inch 
thick, interposed. The connecting rod is 6 feet long between 
the centres, and is fitted with bushes of white metal. The 
eccentrics are formed of wrought iron, and have 4^ inches of 
throw. The link of the link motion is formed of wrought iron. 



SAFETY VALVES AND FEED PUMPS. 



337 



It is hung by a link from a pin attached to tlie framing ; and 
instead of being susceptible of upward and downward motion, 
as in the case of the link represented in Jig, 57 a rod connecting 
the valve rod with the movable block in the link, is susceptible 
of this motion, whereby the same result is arrived at as if the 
link were moved and the block was stationary. One or the 
other expedient is preferable, according to the general nature 
of the arrangements adopted. The slide valve is of brass, and 
the regulator consists of two brass slide valves worked over ports 
in a chest in the steam pipe, set in the smoke box. The steam 
pipe is of brass. No. 14. wire gauge, perforated within the boiler 
barrel with holes Y*2th of an inch in diameter along its upper 
side. The blast pipe, which is of copper, has an rig. 58. 
orifice of 4^ inches diameter. There is a damper, 
formed like a Venetian blind, with the plates run- 
ning athwartships at the end of the tubes. 

662. Q, — Of what construction is the safety 
valve ? 

A, — There are two safety valves, consisting of 
pistons ly^ inch in diameter, and which are kept 
down by spiral springs placed immediately over 
them. A section of this valve is given in Jig, 58. 

663. Q. — What are the dimensions of the feed 
pumps ? 

A. — The feed pumps are of brass, with plung- 
ers 4 inches diameter and 3} inches stroke. The 
feed pipe is of copper, 2 inches diameter. A good 
deal of trouble has been experienced in locomotives 
from the defective action of the feed pump, partly 
caused by the leakage of steam into the pumps, 
which prevented the water from entering them, 
and partly from the return of a large part of 
the water through the valves at the return stroke 




of the pump, in consequence of the valve lifting Gooch. 
too high. The pet cock — a small cock communicating with the 
interior of the pump — will allow any steam to escape which 
gains admission, and the air which enters by the cock cools 



338 TENDENCIES OF IMPROVEMUNT. 

down the barrel of the pump, so that in a short time it will be 
in a condition to draw. The most ordinary species of valve in 
the feed joumps of locomotives, is the ball valve. 

Notwithstanding the excellent performance of the best 
examples of locomotive engines, it is quite certain that there is 
still much room for improvement ; and indeed various sources 
of economy are at present visible, which, if properly developed, 
would materially reduce the expense of the locomotive power. 
In all engines the great source of expense is the fuel; and 
although the consumption of fuel has been greatly reduced 
within the last ten or fifteen years, it is capable of being still 
further reduced by certain easy expedients of improvement, which 
therefore it is important should be universally applied. One of 
these expedients consists in heating the feed water by the waste 
steam ; and the feed water should in every case be sent into the 
boiler lolling hot, instead of being quite cold, as is at present 
generally the case. The ports of the cylinders should be as 
large as possible ; the expansion of the steam should be carried 
to a greater extent ; and in the case of engines with outside 
cylinders, the waste steam should circulate entirely round the 
cylinders before escaping by the blast pipe. The escape of heat 
from the boiler should be more carefully prevented ; and the 
engine should be balanced by weights on the wheels to obviate 
a waste of power by yawing on the rails. The most important 
expedient of all, however, lies in the establishment of a system 
of registering the performance of all new engines, in order that 
competition may stimulate the diflferent constructors to the 
attainment of the utmost possible economy; and under the 
stimulus of comparison and notoriety, a large measure of 
improvement would s^Dcedily ensue. The benefits consequent 
on public competition are abundantly illustrated by the rapid 
diminution of the consumption of fuel in the case of agricultural 
engines, when this stimulus was presented. 



CHAPTER XI. 

ON VARIOUS FORMS, APPLICxVTIONS, AND APPLIANCES 
OF THE STEAM ENGINE. 



In the English edition of this work, the first part of this 
chapter is devoted to examples of Portable and fixed Agri- 
cultural engines, of different makers and styles of workman- 
ship, but not in sufficient detail, nor illustrated on large enough 
scale to be of practical value as models, forming rather in 
fact an illustrated catalogue of the manufacturer, than a study 
for the mechanic. On this account, they have been entirely 
omitted, and their place supplied by a few illustrations from 
American workmanship, not only of Steam Engines, of various 
forms and applications, but also of various machines, or ap- 
pliances, connected with the working of engines, as for the de- 
termination, or regulation of pressure, of the boilers ; for the 
supply or feed of the boilers, the regulation of the speed of the 
engine, and the like. 

The Gauges used in this country to show the pressures of 
steam in boilers are of various constructions, but perhaps the 
most common is the Bourdon, or, as it is known here, the 
Ashcroft gauge, from the party introducing it, and holding 
the patent. Fig 59 represents its interior construction. It con- 
sists of a thin metallic tube, a, bent into nearly a complete circle, 



340 ASHCROFT GAUGE. 

closed at one end, the steam being introduced at the other, 
at 1). The effect of the pressure of the steam on the interior 
of the tube is to expand the circle, more or less according 

Fig. 59. 



to the pressure, the elasticity of the metal returning the circle 
to its original position, when the pressure is removed. The 
free or closed end of the tube is connected by a link c with a 
lever ^, at the opposite end of which is segmental gear, in gear 
with a pinion, on which is a hand, which marks the pressure 
on a dial. The dial and hand are not shown on the cut, but 
are on the exterior case removed to show the construction. 

Fig, 60 is an elevation of a boiler with Clark's Patent Steam 
and Fire Regulator attached, for the control of the draft of 
the chimney by the pressure of steam in the boiler. It consists 
of a chamber, a, with a flexible diaphragm or cover on top, in 
communication with the boiler. On this diaphragm rests a 
plunger or piston, which is held down like a safety valve, by a 
lever and weight, 1). The end of the lever is connected with a 



342 poeter's goyeknor.^ 

balanced damper, c, in the cliimney. The weight, 5, is placed 
at any required position on the lever, and when the pressure 
of steam in the boiler, exerted on the diaphragm, becomes 
sufficient to raise the weight, the lever rises, and the damper 
begins to close, and to check the draft in the chimney. When 
properly adjusted, the machine works on a variation of from 
one to two pounds between the extremes of motion. When 
the dampers are very large, say 3 feet or over, they should be 
set on rollers, like common grindstone rollers ; the regulator 
should be attached directly to the damper, the length of the 
pipe connecting the regulator with the boiler being of no 
account. 

Porter's Patent Governor, fig. 61, is a modification of the 
ordinary centrifugal governor. Very small balls are employed, 
from 2] to 2 1 inches in diameter. These swing from a single 
joint at the axis of the spindle, which is the most sensitive 
arrangement, and make from 300 to 350 revolutions per min- 
ute, at which speed their centrifugal force lifts the counterpoise. 
The lower arms are jointed to the upper ones at the centres of 
the balls, and connect with the slide by joints about two inches 
apart. The counterpoise may be attached to the slide in any 
manner ; for the sake of elegance, it is put in the form of a vase 
rising between the arms, its stem forming the slide. The vase 
is hollow and filled with 1-ead, and weighs from 60 lbs. to 175 
lbs. It moves freely on the spindle, tlyough nearly twice the 
vertical distances traversed by the balls, and is capable of rising 
from 2^ to 3 inches, before its rim will touch the arms. It is 
represented in the figure as lifted through about one half of its 
range of action. 

The standard is bored out of the solid, forming a long and 
perfect bearing for the spindle ; the arms and balls are of gun 
metal, the joint pins of steel ; every part of the governor is 
finished bright, except the bracket carrying the lever, and the 
square base of the standard, which are painted. The pulley 
is from 3 to 10 inches in diameter, and makes in tbe larger sizes 
about 125 revolutions, and in the smaller 230 revolutions per min' 
ute ; the higher speed. of the governor being got up by gearing. 



POKTER S GOYERNOE. 

Fig. 61. 



343 




S44 WOr.THINGTON STEAM PUMP. 

Mr. Porter warrants the following action in tliis governor, 
operating any regulating valve or cut-off wliich is in reasonably- 
good order. The engine should be run with the stop-valve 
wide open, and, except the usual oiling, will require no atten- 
tion from the engineer, under any circumstances, after it is start- 
ed, until it is to be stopped. No increase in the pressure of steam 
will affect its motion perceptibly. The extreme possible varia- 
tion in the speed, between that at which the regulating valve 
will be held wide open, and that at which it will be closed, is 
from 3 to 5 per cent., being least in the largest governors. This 
is less than ^ of the variation required by the average of 
ordinary governors, and is with difficulty detected by the 
senses. The entire load which the engine is capable of driving 
may be thrown on or off at once, and one watching the revolu- 
tions cannot tell when it is done. The governor will be sensibly 
affected by a variation in the motion of the engine of 1 revolu- 
tion in 800. Notwithstanding this extreme sensitiveness, or 
rather by reason of it, it will not oscillate, but when the load is 
uniform will stand quite, or nearly, motionless. 

For the supply of the water to the boiler, in many positions, 
it is very convenient to have a pump unconnected with the 
engine. On this account it is very usual in this country to have 
what are called donkey pumps or engines independent of the 
main engines, which can be used to feed the boilers, or for sup- 
plying water for many other purposes. 

Fig. 62 is a longitudinal section of the Worthington Steam 
Pump, the first of its kind, and for many years in successful 
operation. 

The general arrangement is that of a Steam Cylinder, the 
piston rod of which, carried through into the water cylinder 
and attached directly to the water plunger, works back and 
forth without rotary motion, and of course without using either 
crank or fly wheel. 

In the figures, a is the Steam Cylinder — ^5, the Steam Chest 
— d, a handle for regulating the steam valve—/, the starting 
bar — f7, g, tappets attached to the valve rod, which is moved 
by the contact of the arm <?, on the piston rod with said tappets 



WORTHINGTON^S STEAM PUMP. 




345 



.— ^, the double-acting water plunger working through a pack- 
ing ring — <?, Oj force valves— o, 6, suction valves. The pump 
piston is represented as moving from right to left, the arrows 
indicating the course of the water through the passages. The 
suction valves <5, on the right side, and the force valves <?, on 
the left side, are show open ; a?, is an air chamber made of cop- 



346 



woethington's duplex pump. 



per ; 5, the suction pipe terminating in a vacuum chamber ; 
made by prolonging the suction pipe, and closing it perfectly 
tight at the top, the connection being made to the pump by a 
branch as shown ; w, m, are hand-hole plates, affording easy 
access to the water valves ; n, n, small holes through the plunger, 



Pig. 63. 




GIFFAEd's INJECl'OK. 347 

wMcli relieve the pressure near the end of the stroke, to give 
momentum to throw the valves when working at slow speed. 

Fig. 63 is a perspective view of H. E. Worthington's Duplex 
Steam Pump. The prominent peculiarity of this pump is its 
valve motion. As seen in the cut, two steam pumps are placed 
side by side (or end to end, if desired). Each pump, by a 
rock shaft connected with its piston rod, gives a constant and 
easy motion to the steam valve of the other. Each pump there- 
fore gives steam to and starts its neighbor, and then finishes 
its own stroke, pausing an instant till its own steam valve, 
being opened by the other pump, a-Uows it to make the return 
stroke. 

This combined action produces a perfectly positive valve 
motion without dead points, great regularity and ease of 
motion, and entire absence of noise or shock of any kind. Both 
kinds of pumps are made by Mr. Worthington, of various size 
according to the requirements, the duplex being used for boiler 
feed and for the supply of cities with water. 

Fig. 64 is a side elevation of the Woodward Steam Pump. 
The pump is direct acting. The steam and water piston being 
on the same rod, but momentum is obtained to throw the 
valves by means of a fly wheel, placed beyond the pump, and 
connected with the piston rod by a cross head and a yoke. 
The machine is simple in its construction and action, and is ex- 
tensively used. 

Giffard's Injector, both in Europe and this country, is quite 
extensively used to supply the place of a pump, as independent 
feed for all classes of boilers. It is represented in elevation 
and section, figs. 65 and 66. 

J., steam pipe leading from the boiler. J?, a perforated tube 
or cylinder, through which the steam passes into the space &. (7, 
screwed rod for regulating the passage of steam through the 
annular conical space c, and worked by the handle d. E, suc- 
tion pipe, leading from the tank or hot well to small chamber 
m. F^ annular conical opening or discharge pipe, the size 
of which is regulated by the movement of the tube or cylinder 
B. G, hand wheel for actuating the cylinder B. II, opening, 



348 



woodward's steam pump. 




GIFFARD S INJECTOR. 

Fig. 65. Fig. 66. 



349 




350 giffard's ixjectok. 

in connection with tlie atmosphere, intervening between dis- 
charge pipe F and the receiving pipe through which' the water 
is forced. 7, tube through which the water passes to the 
boiler. K^ valve for preventing the return of the water from 
the boiler when the injector is not working. Z, waste or 
overflow pipe. Jlf, nut to tighten the packing rings g and 
upper packing i in cylinder B, iV, lock nut to hold M, 

The pipe A is connected with the steam space of the boiler 
at its highest part, to obtain as dry steam as possible. The jDas- 
sage of the steam into A is controlled by a cock, as is also the 
feed pipe to the boiler. In working, both are opened, the steam 
passes through A into the space 5, and issuing through the noz- 
zle c with the pressure due to its head, and a partial vacuum by 
its contact with the feed water, it drives this water in connec- 
tion with the jet through the pipe i^into the pipe I in connec- 
tion with the water space of the boiler. 

Method of Working. — Turn the wheel so as to permit a small 
quantity of water to flow to the instrument. Open the steam 
cock connecting the apparatus with the boiler. Turn slightly 
the handle, which will admit a small quantity of steam to the 
apparatus ; a partial vacuum is thus produced, causing the water 
to enter through the supply pipe. As soon as this happens, which 
can be observed at the overflow pipe, the supply of steam or 
water may be increased as required, up to the capacity of the 
instrument, regulating either by means of the wheel and handle, 
so as to prevent any overflow. The quantity of water delivered 
into the boiler, may be varied by means of the stop cocks on 
the steam and water pipes, without altering the handles on the 
injector ; a graduated cock on the water supply pipe is very 
convenient for this purpose. 

The machines are manufactured by Wm. Sellers & Co. 
Philadelphia. 

As an example of Portable Steam Engines, of which there 
are large numbers in this country of different manufacturers, we 
give the representation {fig. 67) of one made by J. C. Hoadley, 
of Lawrence, Mass. 

In these machines, the rules and proportions of the loco- 



r 



hoadley's poetable engine. 



351 




352 hoadley's portable engine. 

motive engine are adapted to the requirements of stationary 
power, for all purposes under forty horse power. The leading 
ideas are : high velocity, high pressure, good valve motion, 
large fire-box, numerous and short flues, and steam blast. The 
characteristic features are : great strength of boiler, fully ade- 
quate to bear with safety 200. lbs. pressure per sq. in., great 
compactness and simplicity, large and adjustable wearing sur- 
faces, and the entire absence of all finish, or polish, for mere 
show. 

The cylinder is placed over the centre of the boiler, at the 
fire-box end, so that the strain due to the engine is central 
to the boiler (which serves as bed plate) ; the starting valve is 
under the hand of the engineer when at the fire door ; and both 
ends of the crank shaft are available for driving pulleys. 

For the sake of compactness, the cylinders are set low, by 
means of a depression in the boiler between the stands of the 
crank shaft, to admit of the play of the crank and connecting 
rod. All the parts are attached to the boiler, which is made of ■ 
sufficient strength to bear all extra strain due to the working 
of the engine. 

They have feed water heater, force pumps, Jackson's governor 
and valve, belt for governor, belt pulley, turned on the face, 
steam gauge ; everything, in short, necessary to the convenient 
working of a steam engine. All engines are fired up and tried 
before they leave the shop, and they are warranted tight, safe, 
and complete. 

A strong and convenient running gear, so arranged as to be 
easily attached and detached at pleasure, is furnished, if de- 
sired ; forming, when separate, a useful wagon. 

Fig. 68 is a compact vertical engine, as built by R. Hoe & 
Co., of this city. It is intended to drive printing presses, but is 
adapted to any kind of work, and is especially suited to such 
places as require economy of space. 



STEAM e:j^gi:i^e of e. hoe & CO. 353 

Fig. es. 




^i^^^^- 



o54 Corliss's steam engine. 

Altliougli the value of expansion lias been called in question 
by some of the engineers of the United States Navy, and under 
an appropriation from Congress is now to be made the subject 
of experimet ; yet, in almost all the manufactories and work • 
shops of the United States, no matter what the form of steam 
engine, or the purposes to which it is applied, whether station- 
ary, locomotive, or marine, some form of cut-off, by which ex- 
pansion of the steam can be availed of, is considered indis- 
pensable. Many varieties are in use, but those engines are most 
poi^ular in which the cut-off is applied directly to the valves on 
the cylinder, opening them quickly and shutting off almost in- 
stantly, avoiding all wire drawing of the steam at the ports, 
and regulating the speed of the engine promptly. Of this 
class of engines, those manufactured by the Corliss Steam En- 
gine Company, of Providence, K. I., are perhaps the widest 
known, not only for their extensive introduction, but also from 
having, by a long and successful litigation, established the 
claims of the patentee, Mr. George II. Corliss. 

Fig, 70 is a section of the cylinder and valve chests of a 
horizontal Corliss engine. 8 is the steam connection, and E tlie 
exhaust ; there are two distinct sets of valves, the steam s, «', and 
the exhaust c^ e\ operated independently of each other. In 
their construction the valves may be considered cylindrical 
plugs, of which portions near the ports are cut away to admit 
the steam and reduce the bearing surface ; the valves are fitted 
on the lathe and the seats by boring. The motion given to the 
valves is rocking, but it will be observed that the valves are not 
firmly connected to the rocking shaft or cylinder ; in the figure 
the valves are shown shade lined, and the shaft or stem plain ; 
in this way the valves are not affected by the packing of the 
valve stem, but always rest upon the face of the jDorts. In the 
figure the piston is just about to commence its outstroke, the 
movement of the steam is supposed to be represented by the 
arrows ; the inner steam valve s, and the outer exhaust e\ are 
just beginning to open. It will be observed that the outer 
steam ^ is fully closed, whilst the inner exhaust valve e is but 
barely so, showing that there has been a cut-off on the steam 



COBLISS'S STEAM ENGINE. 

Fig. 70. 



355 




356 

yalve, but no lead to tlie exliaust, tliat it was left fully open till 
the completion of the stroke. 

Fig, 71 is a side elevation of the cylinder, with the valve 
connections with the governor. S is the steam pipe ; s, «' han- 
dles to the steam valves, and e e' to the exhaust valves, shown in 
dotted line in Jig. 70. The handles to the exhaust valves are 
connected directly to a rocking plate i?, to which motion is given 
by a connection a?, with an eccentric on the engine shaft. When 
once set, therefore the movement of the exhaust valves is con- 
stant, and they will always be opened and closed at the same 
point of the stroke. Connected with the rocking plate R, and 
on opposite sides of its centre, the same as the exhaust valve 
connections, there are two levers, vibrating on a centre c, of 
which one only is shown, as it covers the other ; to the upper 
ends of these levers pawls are attached, one end of which rests 
on the stems or rods connected with the handles s, «', of the 
steam valves ; on these stems there are notches against which 
the pawls strike, and as the levers vibrate inward they push 
back the stems and thereby open the valves, and this continues 
for the whole length of the inward motion of the levers, or till 
the outer extremities of the pawls come in contact with the 
end of the shoi-t lever Z, which, pushing down the outer end 
of the pawls, relieves the stems at the other ends, and the valve 
stem returns to its place through the force of springs attached 
to the outer extremities of the valve stems, a, are cylindrical 
guides to the valve stems, at the inner extremities of which are 
air cushions. The lever I is connected directly with the gov- 
ernor. As the balls rise, they depress the extremity, which cornea 
in contact with the pawls sooner, and thereby shut the valves 
earlier ; and on the contrary when the balls are depressed, the 
valves remain open longer ; as the pawls come in contact with 
the stems always at one point, the steam valves open constantly, 
but are closed at any point by the relief of the paw]"», according 
t/) the speed of the governor. 



COEUSS S STEAM ENGDfE. 

Fi- 7L 



357 




358 WOODRUFF & BEACH S STEAM ENGINE. 

Fig, 71 represents, partly in section and partly in plan, the 
cylinder, steam chests, valves, i&c, of one of the Woodruff & 
Beach high pressure Engines, Wright's patent. 

Fig, 72 represents, in elevation, the cam shaft, to the upper 
end of which, not shown in the drawing, is attached the ordinary 
centrifugal governor. The cylinder, steam chests, valves, &c., 
being similar to those of other engines, need no special notice ; 
but the cam for opening and closing the steam valves, fig, 72, 
requires particular attention, as it embodies a beautiful and 
simple device for cutting off the steam with certainty at any part 
of the stroke, the motion being produced automatically by the 
action of the governor on this cam, throwing it more or less 
out of centre with the spindle of the governor, as the rotation 
of the balls is less or more rapid, the eccentricity of the cam 
determining the amount of steam admitted to the working cylin- 
der of the engine. To produce this effect the cam is made as 
follows : 

(7 is a hollow cylinder or shell, with a part of one end 
formed into a cam proper. Throughout the whole length of 
this piece, upon the inside, there is a spiral groove cut to receive 
one end of a feather, by which its pitch or eccentricity is regu- 
lated. C is also a hollow cylinder or shell, of the same length 
and diameter as (7, with a similar spiral groove cut on the in- 
side, the outside being perfectly smooth and plain, upon which 
the toe {t) for closing the valves is fastened. The inside piece 
consists of two hubs i>, D', eccentric with each other, and made 
in one piece, D being turned to exactly fit the inside of the shell 
(7, and D' to fit the shell G\ the hub D' having a socket (c) into 
which the spindle (s) of the governor is screwed ; the end (d) 
of the hub D forming a journal or beaiing, with a bevel wheel 
on its extremity to convey motion from the crank-shaft gearing 
to the governor and cut-off. There is a hole throughout the 
length of the inside hubs D and D\ which is continued through 
the spindle of the governor, and contains the rod {r) that con- 
nects the cam with the governor. This hole is eccentric to the 
outside surface of the hub i>, as well as to the shell (7, and concen- 
tric with the hub D' and shell G\ and with the governor rod (r). 



WOODRUFF & beach's STEAM ENGIJSTE. 359 

The shell G and liub D, and shell C and hub D\ are con- 
nected together by feathers ; one piece of each feather is of a 
spiral form, and the other a straight or rectangular piece, the 
two being connected together by a stub on the rectangular 
piece, which fits into a hole or bearing in the other or spiral 
piece, so that the latter can turn on the stub and accommo- 
date itself to the groove in which it has to v/ork. The spiral 
part of each feather works in the spiral groove on the inside of 
its corresponding shell G and G' respectively, and the rectangu- 
lar pieces work in a straight groove cut in the hubs D and D\ 
the inner parts of the rectangular pieces being fastened to the 
governor rod (r), so that the feathers are permanently con- 
nected with the governor. 

The shell G' revolves inside of two yokes {y) and {y')^ one 
attached to each steam-valve toe, {a) and {a!) respectively. 

On the inside of each yoke, and opposite to its valve-toe, is a 
raised piece, against which the closing piece {t) on the shell 
( G') acts to close the valves. 

This shell ((7'), as before noticed, has a spiral groove on its 
inside, similar in all respects to that in the cam-shell {G) ; and 
being acted upon in the same manner and through the same rod 
by the governor, it is evident that the closing piece (t) on its 
outside will always hold the same relation to the opening toe 
on the lower or cam-shell ( G) ; and whatever alteration is made 
in the one, a corresponding alteration takes place in the other, 
thereby insuring the closing of the valves at the proper time at 
'Bvery point of the variation of the cut-off. 

When the several pieces above described are put together, 
"the apparatus for opening and closing the valves and producing 
the cut-off is complete, as shown in fig. 72, and it operates as 
follows : • 

Motion is communicated by gearing from the crank-shaft to 
the bevel wheel on the piece {d) on the end of the hub D, and ia 
communicated to the spindle of the governor, which is screwed 
into the socket on D'. As the balls rise or fall, through change 
of centrifugal force due to the variation in the speed of rota- 
tion, they raise or depress the governor-rod, which passea 



360 



WOODRUFF & BEACH S STEAM ENGINE. 




WOODRUFF & beach's STEAM ENGINE. 



361 




^•^ ^^ KJJ 



through the spindle and the hubs D' and JD, and is attached to 
the feathers, thereby raising or depressing the feathers, which, 
acting on their respective spiral grooves, instantly alters the lift 
of the cam on the shell (C), and brings the closing toe (t) on 
the shell (C) into proper position for closing, and so regulates 
the amount of steam admitted to the cylinder. 

Consequently, any speed may be selected at which the load 
of the engine is to move, and any variation from that will be 
instantly felt by the governor, and corrected by this simple and 
beautiful device. There is no jar in the working of the parts ; 
the feathers move noiselessly in their grooves ; the governor rod 
moves up and down through the spindle and the hubs D and 
I>\ and can be regulated by hand to give any required opening 
of the steam ports to suit the work to be done. Any change in 
the amount of work will then alter the speed of the engine, and 
so affect the governor and cam, as before said. 

It is unnecessary to insist on the great economy attained by 
using steam with a well-regulated cut-off, for practical men know ' 
now that the essential points of excellence in the steam engine 
are a good boiler, which generates the greatest quantity of 
steam for the least consumption of fuel ; and, secondly, a 



362 latta's steam fire engine. 

reliable cut-oflf, which uses the steam to the best advantage, by 
admitting the proper quantity for the work required. 

Steam Fire Engines. — Portable engines for the extin- 
guishment of fires, are an American invention, and to Messrs. A. 
B. & E. Latta, of Cincinnati, working on the right principles, 
is due the credit which they claim in their circular, as follows : 

" We claim to be the original and first projectors of the first 
successful steam fire engine in the world^s history. There have 
been many attempts at making a machine of such construction 
as would answer to extinguish fires ; but none of them proved 
to be available in a sufficiently short space of time to warrant 
their use as a fire apparatus. We hold that a steam fire engine 
should be of such nature as to be brought into requisition in as 
short a space of time as is necessary to get the machine on the 
ground, and the hose laid and ready to work : that is, suppos- 
ing the fire to be within one square of the place where the 
steamer is located. The object in locating a machine at any 
point is to protect that immediate vicinity ; and it is therefore 
absolutely necessary to have it available in the shortest space 
of time, and that with unerring certainty. We think that reli- 
ability is of the greatest importance to the protection of a city 
from fire, as everything is dependent on the working of such 
apparatus in time ; and for this reason no expense should be 
spared on this kind of machinery." 

Fig. 73 is a representation of one of the Messrs. Latta's fire 
engines, of which there are many of diiferent classes, according 
to the requirements ; they say that they can furnish engines as 
low as $1,000, and have made some for $10,000. 

The first peculiar feature of this engine is the boiler ; it 
differs entirely from all boilers now in use. 

The fire box or furnace is simply a square box or furnace of 
any required dimensioQS ; it is nothing more than a water space 
surrounding the fire, stay-bolted as all water spaces are. It is 
made of boiler plate in the usual manner. The water space 
extends only f of the height, the balance being a single sheet. 
The bottom of this fire box is crossed l)y grate bars to support 
the fuel ; in its rear side are fire doors, inserted for firing. The 



LATTA'S STEAM FIRE ENGINE. 



363 




364 

internal arrangements of tlie boiler are composed of a large 
number of tubes, lying across in a horizontal position, put to- 
gether in sections with return bends resembling the coils for 
heating buildings. These coils are of small pipe (say one inch 
in diameter), and as numerous as may be necessary. They give 
the required amount of steam. They are secured to wrought- 
iron plates at each end by rivets. These plates lie close to the 
box, and are secured to it, top and bottom. These tubes are 
wrought iron, firmly screwed into the bends, so as to prevent 
any possible breaking. 

The box has a hole through both sheets, in the same man- 
ner as a hollow stay-bolt, through which the coil pij)e passes, 
having no connection with the box. After passing into the 
box it divides into two pipes, then subdivides into four, and so 
on, until its numbers equal the number of coils in the box, and 
to which each limb is attached. The upper ends of these coils 
are the same in number, and are carried through at the top or 
nearly the top of the box. They then nm down outside to the 
steam chamber, or rather water space, as the box is both steam 
chamber and water sj)ace. These pipes empty their contents 
into the box, steam and water, as it may come, all together. It 
will be observed that these coils of tube are sufficiently sep- 
arated to allow the fire to pass between them fi'eely, and cover 
their whole surface. 

The mode of operation of this boiler is this : The fire box 
is filled f full of water. The coils are dry at starting ; the space 
for fuel being filled with good wood, the fire is lighted, and in 
a few moments the engineer moves his hand pump, which takes 
its water from the box to which it is attached, and forces it 
through the coils. By this means steam is generated in from 3 
to 5 minutes, so as to start the engine. 

It will be seen that the water performs a complete circuit; 
it is taken from the box and passed through the coils ; what is 
steam remaias in the steam chamber, and what is not (if any) 
drops back into the box from where it started. Hence it will 
be seen that a large surface is exposed to a small quantity of 
water, and in a way that it is entirely controllable. All the 



AMOSKEAG STEAM FIEE ENGINE. 365 

engineer has to do to surcharge his steam, is to reduce the 
speed of the pump (which is independent of the main engine). 
By raising the heat and quantity of water, any degree of elas- 
ticity can be given to the steam, and that, too, with the least 
amount of waste heat in giving a natural draft. Hence the 
great economy of this boiler. 

The next feature of this engine is, it has no wood work 
about it to perish with the heat and roughness of the streets. 
All the wheels are wrought' iron ; and, as yet, these are the only 
ones that have stood a steam fire engine. The frame is wrought 
iron ; truck, on which the front wheel is hung, wrought iron. 
The axles are cast steel. The engine and pump is a double-acting 
piston pump direct, without any rotary motion ; with a perfect 
balance valve, it is balanced at all times, and hence the engine 
remains quiet without blocking, when at work. The engine is 
mounted on three wheels, which enables it to be turned in a 
very short space. 

Many engines have been constructed by the Messrs. Latta 
for the fire companies of different cities, and have been in suc- 
cessful competition with other engines ; the farthest throw ever 
made by one of their first-class engines was 310 feet from a 
1| inch nozzle ; steaming time, starting from cold water, 3 J min- 
utes. 

Fig. 74 is a representation of one class of steam fire engine, 
as built by the Amoskeag Manufacturing Company, at Man- 
chester, N. H. The boiler is an upright tubular boiler, of a 
peculiar construction, the patent right to which is vested in the 
Amoskeag Manufacturing Company. This boiler is very simple 
in its combination, and for safety, strength, durability, and 
capacity for generating steam is unsurpassed. No fan or arti- 
ficial blower is ever used or needed, the natural draft of the 
boiler being always suflicient. Starting with cold water in the 
boiler, a working head of steam can be generated in less than 
five minutes from the time of kindling the fire. The engine 
" Amoskeag," owned by the city of Manchester, has played two 
streams in three minutes and forty seconds after touching the 
match, at the same time drawing her own water. The boilers 



366 



AMOSKEAG STEA^I FIKE ENGINE. 




AMOSKEAG STEAM EIEE ENGINE, 367 

are made and proved so as to be safely run at a steam pressure 
of 140 to 150 lbs. to the square inch ; but the engines are con- 
structed so as to give the best streams at a pressure of about 
100 lbs. to the square inch, and for service at fires a steam 
pressure of about 60 lbs. to the square inch is all that is re- 
quired. 

The various styles of engine are all vertical in their action, 
and in all the pumps and steam cylinders are firmly and directly 
fastened to the boiler, the steam cylinders being attached direct- 
ly to the steam dome. This arrangement obviates the necessity 
of carrying steam to the cylinders through pipes of considerable 
length, and the machine has very little vibratory motion when 
in operation — so little that it is not necessary to block its wheels 
to keep it in its place, or to take the weight off the springs be- 
fore commencing work. 

The pumps are placed on the engines as near the ground as 
they can be with safety, and are arranged so as to attach the 
suction^ and leading hose to either or both sides of the machine, 
as may be most convenient or desirable, so that less difficulty 
will be found in placing an engine for work, and when required 
to draw its own water, it has only to draw it the shortest pos- 
sible distance. 

Each engine has two " feed pumps " for supplying the boiler, 
and also a connection between the main forcing pumps and the 
boiler, so that it can be supplied from that source if desirable. 
The tank which carries the water for supplying the boiler is so 
placed that the water in it is always above the " feed pumps," 
an advantage that insures the almost certain working of these 
pumps. These pumps are of brass, the best locomotive pattern, 
a?nd one of them running with the engine, wdien at w^ork, fur- 
nishes an ample supply of water to the boiler. 

The engines are exceedingly portable ; they can be turned 
about or placed for service in as contracted a space as any hand 
engine, and two good horses will draw a first-class engine with 
the greatest ease, carrying at the same time water for the boiler, 
a supply of fuel sufficient to run the engine two hours, the 
driver, the engineer, and the fireman. 



368 



STEAM FIRE ENGINE OF 




SILSBEE, MYNDERSE & CO. 369 

Fig, 75 is a representation of the class of steam fire engine 
"built by Silsbee, Mynderse & Co., Seneca Falls, N. Y., under 
Holly's patent. 

The boiler is vertical, with vertical water tubes passing 
directly through the fire. These tubes are closed at the bottom 
and open at the top, where they pass through a water-tight 
plate, and commimicate with the water in the boiler. The 
arrangement of the tubes causes a constant current, the water 
rising on the outside of the tubes as they are heated, and its 
place being supplied by a current flowing downward through 
the tube to the boiler. The smoke and flame pass among the 
tubes up through flues. 

Both engine and pump are rotary, and of the same type. 
They consist essentially of two elliptical rotary pistons, cogged 
and working into one another in an air-tight case. The pistons 
fit close to the inside of the case, and gear into each on the line 
of their conjugate diameters. The action is somewhat similar to 
the old-fashioned rotary pump, consisting of two cog wheels in 
gear with each other, the spaces at the side of the case being 
filled with water, which at the centre are occupied by the teeth 
in gear. In Holly's pump, instead of uniform teeth, and depend- 
ing on the fit of the teeth with the side of the case and with 
each other for the packing, there are two large teeth in each 
piston opposite each other, which have slide pistons, and inter- 
mediate with these large teeth are small cogs, which continue the 
motion of the rotary pistons. The machine works very smoothly, 
and performs the work necessary, in ordinary service, under a 
pressure of 50 to 60 lbs. 

There are many other makers of fire engines iu this country ; 
but suflacient examples are given to illustrate the class ; so suc- 
cessful have they been, that they are fast superseding hand en- 
gines, even in the smaller cities. 

Under a paid department, the following is, in the city of 
Boston, Mass., the comparative cost of running the two kinds 
Df engines, viz. : 



370 COST OF RUNNING FIRE ENGINES. 

STEAM FIRE ENGINE. 

1 engineer $'^20 00 

1 fireman 600 00 

1 driver 600 00 

1 foreman of hose 150 00 

8 hosemen, at $125 each 375 00 

T men $2,445 00 

Keeping of 2 horses 315 00 

Total $2760l0 

HAND ENGINE. 

1 foreman .' ^^^0 00 

1 assistant foreman 125 00 

1 clerk.. 125 00 

1 steward 125 00 

8 leading hosemen, at $125 each 875 00 

33 men, at $100 each 3,300 00 

40 men $^200 00 

Here the engineer, fireman, and driver are constantly em- 
ployed, the hosemen have other employment in the neighbor- 
hood, but all the company sleep in the engine house. 

In the city of Manchester, N. H., a steam fire engine com- 
pany is composed of fourteen men, all told, one of whom, acting 
as driver and steward, is constantly employed, remaining at the 
engine house with a pair of horses always ready to run out 
with the engine in case of an alarm of fire. The other members 
of the company have other employments, and turn out only on 
an alarm of fire. 

STEAM FIRE ENGINES. 

" Amoskeag," Expenditures $504 S2 

"Fire King," " 855 7S 

" E. W. Harrington," « 49G 09 

The above expense includes pay of members, team expenses, 
cost of gas, wood, coal, and all necessities incident to service. 

The " E. W. Harrington " is a second-class engine, stationed 
in the outskirts of the city, and was run cheaper from the fact 
that no horses were kept for it by the city. 

A first-class hand-engine company is allowed to number, all 



f 



OTIS'S EXCAYATOE. 371 

told, fifty men, and the members of the company are paid as 
follows : 

riEST-CLASS HAND-EXGINE COMPANY. 

1 foreman $35 00 

1 assistant foreman 28 00 

1 clerk 28 00 

1 steward 68 00 

46 men, at $18 eacli 828 00 

50 men. Total $987 00 

By this it will be seen that in a city like Manchester, with 
from twenty to twenty-five thousand inhabitants, a first-class 
steam fire engine can be run at an expense not to exceed that 
of a first-class hand engine, while in service it will do at least 
four times the work. The cost of repairs is found by experience 
to be no greater on the steam fire engines than on hand engines. 

The Excavator, Jig. 76, is the invention of the late Mr. Otis, 
an application of the spoon dredging machine of the docks to 
railway purposes, with very important modifications. The 
machine consists of a strong truck, J., A^ mounted on railway 
wheels, on which is placed the boiler (7, the crane E^ and the 
requisite gearing. The excavator or shovel, i), is a box of 
wrought iron, with strong points in front to act as picks in 
loosening the earth, and its bottom hung by a hinge at d^ so 
that, by detaching a catch, it may fly open and discharge the 
material raised. To operate the machine, suppose the shovel D 
to be in the position shown in the cut ; it is lowered by the 
chains <?, ^, and thrown forward or backward, if necessary, by the 
drum B^ and handle 8^ till the picks in the front of the shovel 
are brought in proper contact with the face of the cut ; motion 
forward is now given to the shovel by the drum B and handle 8^ 
and at the same time it is raised by the chains <?, o. These two 
motions can be so adjusted to each other, as to give movement 
to the shovel to enable it to loosen and scrape up a shovelful 
of earth. The handle 8 is now left free, and the shovel D is 
raised vertically by the chains ^, o. The crane is now turned 
round, till the shovel comes over a rail car on a side track ; the 
bottom of the shovel is opened, and the dirt deposited in the 



372 



OTIS S EXCAVATOR. 




POWER NECESSARY FOR THRESHING. 



373 



car. All these motions are performed by the aid of a steam en- 
gine, and are controlled by a man who stands on a platform at/. 

692. Q. — Having now described the most usual and approved 
forms of engines applicable to numerous miscellaneous purposes 
for which a moderate amount of steam power is required, will 
you briefly recapitulate what amount of work of different kinds 
an engine of a given power will perform, so that any one desir- 
ing to employ an engine to perform a given amount of work, 
vfill be able to tell what the power of such engine should be ? 

A,— It will of course be impossible to recapitulate all the 
purposes to which engines are applicable, or to specify for every 
case the amount of power necessary for the accomplishment of 
a given amount of work ; but some examples may be given 
which will be applicable to the bulk of the cases occurring in 
practice. 

693. Q. — Beginning, then, with the power necessary for 
threshing, — a 4 horse power engine, with cylinder 6 inches 
diameter, pressure of steam 45 lbs., per square inch, and making 
140 revolutions per minute, will thresh out 40 quarters of wheat 
in 10 hours with a consumption of 3 cwt. of coals. 

A. — Although this may be done, it is probably too much to 
say that it can be done on an average, and about three fourths 
of a quarter of wheat per horse power would probably be a 
nearer average. The amount of power consumed varies with 
the yield. 

Messrs. Barrett, Exall, and Andrewes give the following 
table as illustrative of the work done, and the fuel consumed 
by their portable engines; but this must be regarded as a 
maximum performance : — 



Number of 
Horse Power. 


Weight of Engine. 


Quarters of Cora 

thrashed in 10 

Hours. 


Quantitv of Coals 

consumer! in 10 

Hours. 


Quantity of Water 

required for 10 
Hours in Gallons. 


4 
5 
6 

7 

8 

10 


Tons. Cwts. 
. 2 
2 5 
2 10 

2 15 

3 
3 10 


40 
50 
60 
70 
80 
100 


Cwts. 
3 
4 
5 
6 
7 
9 


300 
880 
460 
540 
620 
780 



17 



374 POWER REQUIRED FOR GRINDIXG CORN. 

694. Q. — In speaking of horses power, I suppose you mean 
indicator horse power ? 

A. — Yes; or rather the dynamometer horse power, which 
is the same, barring the friction of the engine. At the shows 
of the Royal Agricultural Society, the power actually exerted 
by the different engines is ascertained by the application of a 
friction wheel or dynamometer. 

695. Q. — Can you give any other examples of the power 
necessary for grinding corn ? ■ 

A. — ^An engine exerting 2o\ horses power by the indicator 
works two pairs of flour stones of 4 feet 8 inches diameter, two 
pairs of stones grinding oatmeal of 4 feet 8 inches diameter, one 
dressing machine, one pair of fanners, one dust screen, and one 
sifting machine. One of the flour stones makes 85, and the 
other 90 revolutions in the minute. One of the oatmeal stones 
makes 120, and the other 140 revolutions in the minute. To 
take another case : — An engine exerting 26i indicator horses 
power works two j)airs of flour stones, one dressing machine, 
two pairs of stones grinding oatmeal, and one pair of shelling 
stones. The flour stones, one pair of the oatmeal stones, and 
shelling stones, are 4 feet 8 inches diameter. The diameter 
«if the other pair of oatmeal stones is 3 feet 8 inches. The 
length of the cylinder of the dressing machine is 7 feet 6 inches. 
The flour stones make 87 revolutions in the minute, and the 
larger oatmeal stone 111 revolutions, but the smaller oatmeal 
stone and the shelling stone revolve faster than this. At the 
time the indicator diagram was taken, each pair of flour stones 
was grinding at the rate of 5 bushels an hour ; each pair of 
oatmeal stones about 24 bushels an hour ; and the shelling 
stones were shelling at the rate of about 54 bushels an hour. 
The fanners and screen were also in operation. 

696. Q. — Have you any other case to enumerate ? 

A. — I may mention one in which the power of the same 
engine was increased by giving it a larger supply of steam. 
The engine when working with 8.65 horses power, gives motion 
to one pair of oatmeal stones of 4 feet 6 inches diameter, and 
one pair of ^our stones 4 feet 8 inches diameter. The oatmeal 



POWER REQUIRED FOR SUGAR MILLS. 375 

stone makes 100 revolutions in the minute, and the flour stone 
89. The oatmeal stones grind about 36 bushels in the hour, and 
the flour stones 5 bushels in the hour. The engine when 
working to 12 horses power drives one pair of flour stones, 4 
feet 8 inches diameter, at 89 revolutions per minute and one 
pair of stones of the same diameter at 105 revolutions, grinding 
beans for cattle. The flour mill stones with this proportion of 
power, being more largely fed, ground 6 bushels per hour, and the 
other stones also ground 6 bushds per hour. When the power was 
increased to 18 horses, and the engine was burdened in addition 
with a dressing machine having a cylinder of 19 inches diame- 
ter, the speed of the flour stone fell to 85, and of the beans 
stone to 100 revolutions per minute, and the yield was also 
reduced. The dressing machine dressed 24 bushels per hour. 

697. ^.— What is the power necessary to work a sugar mill 
such as is used to press the juice from canes in the West Indies ? 

A. — Twenty horses power will work a sugar mill having 
rollers about 5 feet long and 28 inches diameter; the rollers 
making 21 turns in a minute. If the rollers be 26 inches diame- 
ter and 4i feet long, 18 horses power will suffice to work them 
at the same speed, and 16 horses power if the length be reduced 
to 3 feet 8 inches. 12 horses power will be required to work a 
sugar mill with rollers 24 inches diameter and 4 feet 2 inches 
long ; and lO horses power will suffice if the rollers be 3 feet 
10 inches long and 23 inches diameter. The speed of the 
surface of sugar mill rollers should not be greater than 16 feet 
per minute, to allow time for the canes to part with their juice. 
In the old mills the speed was invariably too great. The 
quantity of juice expressed will not be increased by increasing 
the speed of the rollers, but more of the juice will pass away in 
the begass or woody refuse of the cane. 

698. Q. — What is the amount of power necessary to drive 
cotton mills ? 

A. — An indicator or actual horse power will drive 305 hand 
mule spindles, with proportion of preparing machinery for the 
same ; or 230 self-acting mule spindles with preparation ; or 104 
throstle spindles with preparation ; or 10| power looms with 



376 POWER REQUIRED FOR SPINNING AND SAWING. 

common sizing. The throstles referred to are the common thros- 
tles spinning 34's twist for power loom weaving, and the spin- 
dles make 4000 turns per minute. The self-acting mules are 
Robert's, about one half spinning 36's weft, and spindles revolv- 
ing 4800 turns per minute ; and the other half spinning 36's 
twist, with the spindles revolving 5200 times per minute. 
Half the hand mules were spinning 36's weft, at 4700 revolutions, 
and the other half 36's twist at 5000 revolutions per minute. 
The average breadth of the looms was 37 inches, weaving 37 
inch cloth, making 123 picks per minute, — all common calicoes 
about 60 reed, Stockport count, and 68 picks to the inch. To 
take another example in the case of a mill for twisting cotton 
yarn into thread : — In this mill there are 27 frames with 96 
common throstle spindles in each, making in all 2592 spindles. 
The spindles turn 2200 times in a minute ; the bobbins are 1| 
inches diameter, and the part which holds the thread is 2^^ 
inches long. In addition to the twisting frames the steam 
engine works 4 turning lathes, 3 polishing lathes, 2 American 
machines for turning small bobbins, two circular saws, one of 
22 and the other of 14 inches diameter, and 24 bobbin heads 
or machines for filling the bobbins with finished thread. The 
power required to drive the whole of this machinery is 28J 
horses. When all the machinery except the spindles is thrown 
off, the power required is 21 horses, so that 2592, the total num- 
ber of spindles, divided by 21, the total power, is the number 
of twisting spindles worked by each actual horse power. The 
number is 122.84. 

699. Q. — What work will be done by a given engine in 
sawing timber, pressing cotton, blowing furnaces, driving piles, 
and dredging earth out of rivers ? 

A.— A high pressure cylinder 10 inches diameter, 4 feet 
stroke, making 35 revolutions with steam of 90 to 100 lbs. on 
the square inch, supplied by three cylindrical boilers 30 inches 
diameter and 20 feet long, works two vertical saws of 34 inches 
stroke, which are capable of cutting 30 feet of yellow pine, 18 
inches deep, in the minute. A high pressure cylinder 14 inches 
diameter and 4 feet stroke, making 60 strokes per minute with 



PEESSixG cotto:n^, blowing furnaces, etc. 377 

steam of 40 lbs. on the square inch, supplied by three cylindrical 
boilers without flues, 30 inches diameter and 26 feet long, with 
32 square feet of grate surface, works four cotton presses geared 
6 to 1, with two screws in each of 7i inches diameter and 1| 
pitch, which presses will screw 1000 bales of cotton in the 
twelve hours. Also one high pressure cylinder of 10 inches 
diameter and 3 feet stroke, making 45 to 60 revolutions per 
minute, with steam of 45 to 50 lbs. per square inch, with two 
hydraulic presses having 12 inch rams of 4^ feet stroke, and 
force pumps 2 inches diameter and 6 inches stroke, presses 30 
bales of cotton per hour. One condensing engine with cylinder 
56 inches diameter, 10 feet stroke, and making 15 strokes per 
minute with steam of 60 lbs. pressure per square inch, cut off 
at Jth of the stroke, supplied by six boilers, each 5 feet diame- 
ter, and 24 feet long, with a 22-inch double-return flue in each, 
and 198 square feet of fire grate, works a blast cylinder of 126 
inches diameter, and 10 feet stroke, at 15 strokes per minute. 
The pressure of the blast is 4 to 5 lbs. per square inch ; the area 
of pipes 2300 square inches, and the engine blows four furnaces 
of 14 feet diameter, each making 100 tons of pig iron per week. 
Two high pressure cylinders, each of 6 inches diameter and 18 
inches stroke, making 60 to 80 strokes per minute, with steam 
of 60 lbs. per square inch, lift two rams, each weighing 1000 
lbs., ^ye times in a minute, the leaders for the lift being 24 feet 
long. One high pressure cylinder of 12 inches diameter and 5 
feet stroke, making 20 strokes per minute, with steam of 60 to 
70 lbs. pressure per square inch, lifts 6 buckets full of dredging 
per minute from a depth of 30 feet below the water, or lifts 10 
buckets full of mud per minute from a depth of 18 feet below 
the water. 



CHAPTER Xn. 

MANUFACTURE AND MANAGEMENT OF STEAM ENGINES. 



CONSTRUCTION OF ENGINES. 

700. Q. — ^Wbat are the qualities whicli should be possessed 
by the iron of which the cylinder of steam engines are made ? 

A. — The general ambition in making cylinders is to make 
them sound and hard ; but it is expedient also to make them 
tough, so as to approach as nearly as possible to the state of 
malleable iron. This may be done by mixing in the furnace as 
many different kinds of iron as possible ; and it may be set 
down as a general rule in iron founding, that the greater the 
number of the kinds of metal entering into the composition of 
any casting, the denser and tougher it will be. The constituent 
atoms of the different kinds of iron appear to be of different 
sizes, and the mixture of different kinds maintains the tough- 
ness, while it adds to the density and cohesive power. Hot 
blast iron was at one time generally believed to be weaker than 
cold blast iron, but it is now questioned whether it is not the 
btronger of the two. The cohesive strength of unmixed iron is 
not in proportion to its specific gravity, and its elasticity and 
power to resist shocks appear to become greater as the specific 
gravity becomes less. Nos. 3 and 4 are the strongest irons. In 
most cases, iron melted in a cupola is not so strong as when 



PKOCESS OF casti:n'g cylinders. 379 

remelted in an air furnace, and when run into green sand it is 
not reckoned so strong as when run into dry sand, or loam. 
The quality of the fuel, and even the state of the weather, 
exerts an influence on the quality of the iron : smelting fur- 
naces, on the cold blast principle, have long been known to 
yield better iron in winter than in summer, probably from the 
existence of less moisture in the air ; and it would probably be 
found to accomplish an improvement in the quality of the iron 
if the blast were made to pass through a vessel containing muri- 
ate of lime, by which, the moisture of the air would be extracted. 
The expense of such a preparation would not be considerable, 
as, by subsequent evaporation, the salt might be used over and 
over again for the same purpose. 

701. Q. — Will you explain the process of casting cylinders ? 

A. — The mould into which the metal is poured is built up 
of bricks and loam, the loam being clay and sand ground to- 
gether in a mill, with the addition of a little horse-dung to give 
it a fibrous structure and prevent cracks. The loam board, by 
which the circle of the cylinder is to be swept, is attached to an 
upright iron bar, at the distance of the radius of the cylinder, 
and a cylindrical shell of brick is built up, which is plastered 
on the inside with loam, and made quite smooth by traversing 
the perpendicular loam board round it. A core is then formed 
in: a similar manner, but so much smaller as to leave a space be- 
tween the shell and the core equal to the thickness of the cylin- 
der, and into this space the melted metal is poured. Whatever 
nozzles or projections are required upon the cylinder, must be 
formed by means of wooden patterns, w^hich are built into the 
shell, and subsequently withdrawn ; but where a number of 
cylinders of the same kind are required, it is advisable to make 
these patterns of iron, which will not be liable to warp or twist 
while the loam is being dried. Before the iron is cast into the 
mould, the interior of the mould must be covered with finely 
powdered charcoal — or blackening, as it is technically termed ; 
and the secret of making finely skinned castings lies in using 
plenty of blackening. In loam and dry sand castings the char- 
coal should be mixed with thick clay water, and applied until 



380 PROCESS OF BOKING CYLINDERS. 

it is an eighth of an inch thick, or more ; the surface should be 
then very carefully smoothed or sleeked, and if the metal has 
been judiciously mixed, and the mould thoroughly dried, the 
casting is sure to be a fine one. Dry sand and loam castings 
should be, as much as possible, made in boxes ; the moulds may 
thereby be more rapidly and more effectually dried, and better 
castings will be got with a less expense. 

702. Q. — Will you explain the next operation which a cylin- 
der undergoes ? 

A. — The next stage is the boring ; and in boring cylinders 
of 74 inches diameter, the boring bar must move so as to make 
one revolution in about 4|- minutes, at which speed the cutters 
will move at the rate of about 5 feet per minute. In boring 
brass, the speed must be slower ; the common rate at which the 
tool moves in boring brass air pumps is about 3 feet per minute. 
If this speed be materially exceeded the tool will be spoiled, 
and the pump made taper. The speed proper for boring a 
cylinder will answer for boring the brass air pump of the same 
engine. A brass air pump of 36^ inches diameter requires the 
bar to make one turn in about three minutes, which is also the 
speed proper for a cylinder 60 inches in diameter. To bore a 
brass air pump 36^ inches in diameter requires a week, an iron 
one requires 48 hours, and a copper one 24 hours. In turning a 
malleable iron shaft 12| inches in diameter, the shaft should 
make about five turns per minute, which is equivalent to a 
speed in the tool of about 16 feet per minute ; but this speed 
may be excee^led if soap and water be plentifully run on the 
point of the tool. A boring mill, of which the speed may be 
varied from one turn in six minutes to twenty-five turns in one 
minute, will be suitable for all ordinary wants that can occur in 
practice. 

703. Q, — ^Are there any precautions necessary to be observed 
in order that the boring may be truly effected ? 

A. — In fixing a cylinder into the boring mill, great care 
must be taken that it is not screwed down unequally ; and in- 
deed it will be impossible to bore a large cylinder in a horizon- 
tal mill without being oval, unless the cylinder be carefully 



PEOCESS OF CONSTEUCTING PISTONS. 381 

gauged when standing on end, and be set up by screws wlien 
laid in the mill until it again assumes its original form. A large 
cylinder will inevitably become oval if laid upon its side ; and 
if while under the tension due to its own weight it* be bored 
round, it will become oval again when set upon end. If the bot- 
tom be cast in, the cylinder will be probably found to be round 
at one end and oval at the other, unless a vertical boring mill 
be employed, or the precautions here suggested be adopted. 

704. Q, — Does the boring tool make the cylinder sufficiently 
smooth for the reception of the piston ? 

A, — ^Many engine makers give no other finish to their cylin- 
ders ; but Messrs. Penn grind their cylinders after they are 
bored, by laying them on their side, and rubbing a piece of 
lead, with a cross iron handle like that of a rolling stone, and 
smeared with emery and oil, backward and forward — ^the cylin- 
der being gradually turned round so as to subject every part 
successively to the operation. The lead by whixjh this grinding 
is accomplished is cast in the cylinder, whereby it is formed of 
the right curve ; but the part of the cylinder in which it is cast 
should be previously heated by a hot iron, else the metal may 
be cracked by the sudden heat. 

705. Q.— How are the parts of a piston fitted together so as 
to be perfectly steam tight ? 

A. — The old practice was to depend chiefly upon grinding 
as the means of making the rings tight upon the piston or upon 
one another; but scraping is now chiefly relied on. Some 
makers, however, finish their steam surfaces by grinding them 
with powdered Turkey stone and oil. A slight grinding, or 
polishing, with powdered Turkey stone and oil, appears to be 
expedient in ordinary cases, and may be conveniently accom- 
plished by setting the piston on a revolving table, and holding 
the ring stationary by a cross piece of wood while the table 
turns round. Pieces of wood may be interposed between the 
ring and the body of the piston, to keep the ring nearly in its 
right position ; but these pieces of wood should be fitted so 
loosely as to give some side play, else the disposition would 
arise to wear, the flange of the piston into a groove. 



382 DIRECTIONS FOR ACCURATE FITTING. 

706. §.— What kind of tool is used for finishing surfaces by 
scraping ? 

A,—K flat file bent, and sharpened at the end, makes an 
eligible scraper for the first stages ; or a flat file sharpened at the 
end and used like a chisel for wood. A three-cornered file, 
sharpened at all the corners, is the best instrument for finishing 
the operation. The scraping tool should be of the best steel, 
and should be carefully sharpened at short intervals on a Tur- 
key stone, so as to maintain a fine edge. 

707. §.— Will you explain the method of fitting together 
the valve and cylinder faces ? 

^.— Both faces must first be planed, then filed according to 
the indications of a metallic straight edge, and subsequently of a 
thick metallic face plate, and finally scraped very carefully until 
the face plate bears equally all over the surface. In planing any 
surface, the catches which retain the surface on the planing ma- 
chine should be relaxed previously to the last cut, to obviate dis- 
tortion from springing. To ascertain whether the face plate bears 
equally, smear it over with a little red ochre and oil, and move 
the face plate slightly, which will fix the color upon the promi- 
nent points. This operation is to be repeated frequently ; and 
as the work advances, the quantity of coloring matter is to be 
diminished, until finally it is spread over the face plate in a 
thin film, which only dims the brightness of the plate. The 
surfaces at this stage must be rubbed firmly together to make 
the points of contact visible, and the higher points will become 
slightly clouded, while the other parts are left more or less in 
shade. If too small a quantity of coloring matter be used at 
first, it will be difficult to form a just conception of the general 
state of the surface, as the prominent points will alone be indi- 
cated, whereas the use of a large quantity of coloring matter in 
the latter stages would destroy the delicacy of the test the face 
plate afi'ords. The number of bearing points which it is desir- 
able to establish on the surface of the work, depends on the use 
to which the surface is to be applied ; but whether it is to be 
finished with great elaboration, or otherwise, the bearing points 
should be distributed equally over the surface. Face plates, or 



DIRECTION FOR FACING CYLINDERS. 383 

planotneters, as they are sometimes termed, are supplied by- 
most of the makers of engineering tools. Every factory should 
be abundantly supplied with them, and also with steel straight 
edges ; and there should be a master face plate, and a master 
straight edge, for the sole purpose of testing, from time to time, 
the accuracy of those in use. 

708. Q, — Is the operation of surfacing, which you have de- 
scribed, necessary in the case of all slide valves ? 

A. — Yes ; and in fitting the faces of a D valve, great care 
must, in addition, be taken that the valve is not made conical ; 
for unless the back be exactly parallel with the face, it will be 
impossible to keep the packing from being rapidly cut away. 
When the valve is laid upon the face plate, the back must be 
made quite fair along the whole length, by draw filing, accord- 
ing to the indications of a straight edge ; and the distance from 
the face to the extreme height of the back must be made iden- 
tical at each extremity. 

709. Q. — When you described the operation of boring the cyl- 
inder, you stated that the cylinder, when laid upon its side, became 
oval ; will not this change of figure distort the cylinder face ? 

A, — It is not only in the boring of the cylinder that it is 
necessary to be careful that there is no change of figure, for it 
will be impossible to face the valves truly in the case of large 
cylinders, unless the cylinder be placed on end, or internal props 
be introduced to prevent the collapse due to the cylinder's 
weight. It may be added, that the change of figure is not in- 
stantaneous, but becomes greater after some continuance of the 
strain than it was at first, so that in gauging a cylinder to ascer- 
tain the diiFerence of diameter when it is placed on its side, it 
should have lain some days upon its side to ensure the accuracy 
of the operation. 

710. Q. — How is any flaw in the valve or cylinder face rem- 
edied ? 

A. — Should a hole occur either in 'the valve, in the cylinder, 
or any other part where the surface requires to be smooth, it 
may be plugged up with a piece of cast iron, as nearly as pos- 
sible of the same texture. Bore out the faulty part, and after- 



384 PREPARATION OF THE VAI.YE FACES. 

ward widen the hole with an eccentric drill, so that it will be 
of the least diameter at the mouth. The hole may go more 
than half through the iron : fit then a plug of cast iron roughly 
by filing, and hammer it into the hole, whereby the plug will 
become riveted in it, and its surface may then be filed smooth. 
Square pieces may be let in after the same fashion, the hole 
being made dovetailed, and the pieces thus fitted will never 
come out. 

711. Q. — When cylinders are faced with brass, how is the 
face attached to the cylinder ? 

A, — Brass faces are put upon valves or cylinders by means 
of small brass screws tapped into the iron, with conical necks 
for the retention of the brass : they are screwed by means of a 
square head, which, when the screw is in its place, is cut off and 
filed smooth. In some cases the face is made of extra thickness, 
and a rim not so thick runs round it, forming a step or recess 
for the reception of brass rivets, the heads of which are clear 
of the face. 

712. Q. — What is the best material for valve faces ? 

A, — Much trouble is experienced with every modification of 
valve face ; but cast iron working upon cast iron is, perhaps, 
the best combination yet introduced. A usual practice is to 
pin brass faces on the cylinder, allowing the valve to retain its 
cast iron face. Some makers employ brass valves, and others 
pin brass on the valves, leaving the cylinder with a cast iron 
face. If brass valves are used, it is advisable to plane out two 
grooves across the face, and to fill them up with hard cast iron 
to prevent rutting. Speculum metal and steel have been tried 
for the cylinder faces, but only with moderate success. In some 
cases the brass gets into ruts ; but the most prevalent afiection 
is a degradation of the iron, owing to the action of the steam, 
and the face assuming a granular appearance, something like 
loaf sugar. This action shows itself only at particular spots, 
and chiefly about the angles of the port or valve face. At first 
the action is slow ; but when once the steam has worked a 
passage for itself, the cutting away becomes very rapid, and, in 
li short time, it will be impossible to prevent the engine from 



HOW TO MAKE RUST JOINTS. 385 

heating when stopped, owing to the leakage of steam through 
the valve into the condenser. Copper steam pipes seem to have 
some galvanic action on valve faces, and malleable iron pipes 
have sometimes been substituted ; but they are speedily worn 
out by oxidation, and the scales of rust which are carried on by 
the steam scratch the valves and cylinders, so that the use of 
copper pipes is the least evil. 

713. Q. — Will you explain in what manner the joints of an 
engine are made ? 

A. — Eust joints are not now much used in engines of any 
kind, yet it is necessary that the engineer should be acquainted 
with the manner of their formation. One ounce of sal-ammoniac 
in powder is mingled with 18 ounces or a pound of borings of 
cast iron, and a sufficiency of water is added to wet the mixture 
thoroughly, which should be done some hours before it is wanted 
for use. Some persons add about half an ounce of flowers of 
brimstone to the above proportions, and a little sludge from the 
grindstone trough. This cement is caulked into the joints with 
a caulking iron, about three quarters of an inch wide and one 
quarter of an inch thick, and after the caulking is finished the 
bolts of the joints may be tried to see if they cannot be further 
tightened. The skin of the iron must, in all cases, be broken 
where a rust joint is to be made ; and, if the place be greasy, 
the surface must be well rubbed over with nitric acid, and then 
washed with water, till no grease remains. The oil about en- 
gines has a tendency to damage rust joints by recovering the 
oxide. Coppersmiths staunch the edges of their plates and 
rivets by means of a cement formed of pounded quicklime, 
with serum of blood, or white of egg ; and in copper boilers 
such a substance may be useful in stopping the impalpable 
leaks which sometimes occur, though Roman cement appears to 
be nearly as effectual. 

714. Q. — Will you explain the method of case hardening the 
parts of engines ? 

A. — The most common plan for case hardening consists in 
the insertion of the articles to be operated upon among horn or 
leather cuttings, bone dust, or animal charcoal, in an iron box 



386 SCRAP IRON BAD FOR CASE HARDENING. 

provided with a tight lid, which is then put into a furnace for a 
period answerable to the depth of steel required. In some cases 
the plan pursued by the gunsmiths may be employed with con- 
venience. The article is inserted in a sheet iron case amid bone 
dust, often not burned ; the lid of the box is tied on with wire, 
and the joint luted with clay ; the box is heated to redness as 
quickly as possible and kept half an hour at a uniform heat : its 
contents are then suddenly immersed in cold water. The more 
unwieldy portions of an engine may be case hardened by prus- 
siate of potash — a salt made from animal substances, composed 
of two atoms of carbon and one of nitrogen, and which oper- 
ates on the same principle as the charcoal. The iron is heated 
in the fire to a dull red heat, and the salt is either sprinkled 
upon it or rubbed on in a lump, or the iron is rubbed in the salt 
in powder. The iron is then returned to the fire for a few min- 
utes, and finally immersed in water. By some persons the salt 
is supposed to act unequally, as if there were greasy spots upon 
the iron which the salt refused to touch, and the eff'ect under 
any circumstances is exceedingly superficial ; nevertheless, upon 
all parts not exposed to wear, a sufficient coating of steel may 
be obtained by this process. 

715. Q, — What kind of iron is most suitable for the working 
parts of an engine ? 

A. — In the malleable iron work of engines scrap iron has 
long been used, and considered preferable to other kinds ; but 
if the parts are to be case hardened, as is now the usual practice, 
the use of scrap iron is to be reprehended, as it is almost sure to 
make the parts twist in the case hardening process. In case 
hardening, iron absorbs carbon, which causes it to swell ; and 
as some kinds of iron have a greater capacity for carbon than 
other kinds, in case hardening they will swell more, and any 
such unequal enlargement in the constituent portions of a piece 
of iron will cause it to change its figure. In some cases, case 
hardening has caused such a twisting of the parts of an engine, 
that they could not afterward be fitted together ; it is prefer- 
able, therefore, to make such parts as are to be case hardened 
to any considerable depth of Lowmoor, Bowling, or Indian 



COMPOSITION OF METAL FOR BEARINGS. 387 

iron, wliich being homogeneous will absorb carbon equally, and 
will not twist. 

716. Q, — What is the composition of the brass used for en- 
gine bearings ? 

A. — The brass bearings of an engine are composed princi- 
pally of copper and tin. A very good brass for steam engine 
bearings consists of old copper 112 lbs., tin 12 J lbs., zinc 2 or 3 
oz. ; and if new tile copper be used, there should be 13 lbs. of 
tin instead of 12^ lbs. A tough brass for engine work consists 
of li lb. tin, 1^ lb. zinc, and 10 lbs. copper; a brass for heavy 
bearings, 2^ oz. tin, ^ oz. zinc, and 1 lb. copper. There is a 
great difference in the length of time brasses wear, as made by 
different manufacturers ; but the difference arises as much from 
a different quantity of surface, as from a varying composition 
of the metal. Brasses should always be made strong and thick, 
as when thin they collapse upon the bearing and increase the 
fiiction and the wear. 

717. Q. — How is Babbitt's metal for lining the bushes of 
machinery compounded ? 

A. — Babbitt's patent lining metal for bushes has been 
largely employed in the bushes of locomotive axles and other 
machinery : it is composed of 1 lb. of copper, 1 lb. regulus of 
antimony, and 10 lbs. of tin, or other similar proportions, the 
presence of tin being the only material condition. The copper 
is first melted, then the antimony is added, with a small propor- 
tion of tin — charcoal being strewed over the surface of the 
metal in the crucible to prevent oxidation. The bush or article 
to be lined, having been cast with a recess for the soft metal, is 
to be fitted to an iron mould, formed of the shape and size of 
the bearing or journal, allowing a little in size for the shrinkage. 
Drill a hole for the reception of the soft metal, say | to f inch 
diameter, wash the parts not to be tinned with a clay wash to 
prevent the adhesion of the tin, wet the part to be tinned with 
alcohol, and sprinkle fine sal-ammoniac upon it ; heat the article 
until fumes arise from the ammonia, and immerse it in a kettle 
of Banca tin, care being taken to prevent oxidation. When 
sufficiently tinned, the bush should be soaked in water, to take 



388 COMPOSITION OF VARIOUS ALLOTS. 

off any particles of ammonia that may remain upon it, as the 
ammonia would cause the metal to blow. Wash with pipe 
clay, and dry ; then heat the bush to the melting point of tui, 
wipe it clean, and pour in the metal, giving it sufficient head as 
it cools ; the bush should then be scoured with fine sand, to 
take off any dirt that may remain upon it, and it is then fit for 
use. This metal wears for a longer time than ordinary gun 
metal, and its use is attended with very little friction. If the 
bearing heats, however, from the stopping of the oil hole or 
otherwise, the metal will be melted out. A metallic grease, 
containing particles of tin in the state of an impalpable powder, 
would probably be preferable to the lining of metal just de- 
scribed. 

718. Q. — Can you state the composition of any other alloys 
that are used in engine work ? 

A. — The ordinary range of good yellow brass that files and 
turns well, is about 4^ to 9 ounces of zinc to the pound of cop- 
per. Flanges to stand brazing may be made of copper 1 lb., 
zinc \ oz., lead f oz. Brazing solders when stated in the order 
of their hardness are : — ^three parts copper and one part zinc 
(very hard), eight parts brass and one part zinc (hard), six 
parts brass, one part tin, and one part zinc (soft) ; a very com- 
mon solder for iron, copper, and brass, consists of nearly equal 
parts of copper and zinc. Muntz's metal consists of forty parts 
zinc and sixty of copper ; any proportions between the extremes 
of fifty parts of zinc and fifty parts copper, and thirty-seven 
zinc and sixty-three copper, will roll and work at a red heat, but 
forty zinc to sixty copper are the proportions preferred. Bell 
metal, such as is used for large bells, consists of 4| ounces to 5 
ounces of tin to the pound of copper ; speculum metal consists 
of from 7^ ounces to 8 J ounces of tin to the pound of copper. 

ERECTION" OF ENGINES. 

719. Q. — Wni you explain the operation of erecting a pair 
of side lever engines in the workshop ? 

A, — In beginning the erection of side lever marine engines in 



MODE OF ERECTING ENGINES. 389 

the workshop, the first step is to level the bed plate lengthways 
and across, and strike a line up the centre, as near as possible in 
the middle, which indent with a chisel in various places, so that 
it may at any time be easily found again. Strike another line 
at right angles with this, either at the cylinder or crank centre, 
by drawing a perpendicular in the usual manner. Lay the 
other sole plate alongside at the right distance, and strike a 
line at the cylinder or crank centre of it also, shifting either sole 
plate a little endways until these two transverse lines come into 
the same line, which may be ascertained by applying a straight 
edge across the two sole plates. Strike the rest of the centres 
across, and drive a pin into each corner of each sole plate, which 
file down level, so as to serve for points of reference at any 
future stage ; next, try the cylinder, or plumb it on the inside 
roughly, and see how it is for height, in order to ascertain 
whether much will be required to be chipped off the bottom, or 
whether more requires to be chipped off the one side than the 
other. Chip the cylinder bottom fair ; set it in its place, plumb 
the cylinder very carefully with a straight edge and silk thread, 
and scribe it so as to bring the cylinder mouth to the right 
height, then chip the sole plate to suit that height. The cyliur 
der must then be tried on again, and the parts filed wherever 
they bear hard, until the whole surface is well fitted. Next, 
chip the place for the framing ; set up the framing, and scribe 
the horizontal part of the jaw with the scriber used for the bot- 
tom of the cylinder, the upright part being set to suit the shaft 
centres, and the angular flange of cylinder, where the stay is 
attached, having been previously chipped plumb and level. 
The stake wedges with which the framing is set up preparato^ 
rily to the operation of scribing, must be set so as to support 
equally the superincumbent weight, else the framing will spring 
from resting unequally, and it will be altogether impossible to 
fit it well. These directions obviously refer exclusively to the 
old description of side lever engine with cast iron framing ; but 
there is more art in erecting an engine of that kind with ac- 
curacy, than in erecting one of the direct action engines, where 
it is chiefly turned or bored surfaces that have to be dealt with. 



S90 HOW TO FIX POSITION OF CENTRES. 

720. 6.— How do you lay out the positions of the centres of 
a side lever engine ? 

A. — In fixing the positions of the centres in side lever en- 
gines, it appears to be the most convenient way to begin with 
the main centre. The height of the centre of the cross head at 
half stroke above the plane of the main centre is ^xed by the 
drawing of the engine, which gives the distance from the cen- 
tre of cross head at half stroke to the flange of the cylinder ; 
and from thence it is easy to find the perpendicular distance 
from the cylinder flange to the plane of the main centre, merely 
by putting a straight edge along level, from the position of the 
main centre to the cylinder, and measuring from the cylinder 
flange down to it, raising or lowering the straight edge until it 
rests at the proper measurement. The main centre is in that 
plane, and the fore and aft position is to be found by plumbing 
up from the centre line on the sole plate. To find the paddle 
shaft centre, plumb up from the centre line marked on the edge 
of the sole plate, and on this line lay off from the plane of the 
main centre the length of the connecting rod, if that length be 
already fixed, or otherwise the height fixed in the drawing of 
the paddle shaft above the main centre. To fix the centre for 
the parallel motion shaft, when the parallel bars are connected 
with the cross head, lay off from the plane of main centre the 
length of the parallel bar from the centre of the cylinder, deduct 
the length of the radius crank, and plumb up the central line 
of motion shaft ; lay off on this line, measuring from the plane 
of main centre, the length of the side rod ; this gives the centre 
of parallel motion shaft when the radius bars join the cross 
head, as is the preferable practice where parallel motions are 
used. The length of the connecting rod is the distance from the 
centre of the beam when level, or the plane of the main centre, 
to the centre of the paddle shaft. The length of the side rods 
is the distance from the centre line of the beam when level, to 
the centre of the cross head when the piston is at half stroke. 
The length of the radius rods of the parallel motion is the dis- 
tance from the point of attachment on the cross head or side 
rod, when the piston is at half stroke, to the extremity of the 



HOW TO ADJUST PARALLEL MOTION. 391 

radius crank when the crank is horizontal ; or in engines with 
the parallel motion attached to the cross head, it is the distance 
from the centre of the pin of the radius crank when horizontal 
to the centre of the cylinder. Having fixed the centre of the 
parallel motion shaft in the manner just described, it only re- 
mains to put the parts together when the motion is attached to 
the cross head ; but when the motion is attached to the side 
rod, the end of the parallel bar must not move in a perpendicu- 
lar line, but in an arc, the versed sine of which bears the saHie 
ratio to that of the side lever, that the distance from the top of 
the side rod to the point of attachment bears to the total length 
of the side rod. 

721. Q. — How do you ascertain the accuracy of the parallel 
motion ? 

A. — The parallel motion when put in its place should be 
tested by raising and lowering the piston by means of the 
crane. First, set the beams level, and shift in or out the motion 
shaft plummer blocks or bearings, until the piston rod is up- 
right. Then move the piston to the two extremes of its motion. 
If at both ends the cross head is thrown too much out, the stud 
in the beam to which the motion side rod is attached is too far 
out, and must be shifted nearer to the main centre ; if at the 
extremities the cross head is thrown too far in, the stud in the 
beam is not out far enough. Jf the cross head be thrown in at 
the one end, and out equally at the other, the fault is in the 
motion side rod, which must be lengthened or shortened, to 
remedy the defect. 

722. §.— "Will you describe the method pursued in erecting 
oscillating engines ? 

^.— The columns here are of wrought iron, and in the case 
of small engines there is a template made of wood and sheet 
iron, in which the holes are set in the proper positions, by 
which the upper and lower frames are adjusted ; but in the 
case of large engines, the holes are set off by means of trammels. 
The holes for the reception of the columns are cast in the frames, 
and are recessed out internally : the bosses encircling the holes 
are made quite level across, and made very true with a face 



392 HOW TO ERECT OSCILLATING ENGINES. 

plate, and the pillars which have been turned to a gauge arc 
then inserted. The top frame is next put on, and must bear 
upon the collars of the columns so evenly, that one of the col- 
umns will not be bound by it harder than another. If this 
point be not attained, the surfaces must be further scraped, 
until a perfect fit is established. The whole of the bearings in 
the best oscillating engines are fitted by means of scraping, and 
on no other mode of fitting can the same reliance be placed for 
exactitude. 

723. Q. — How do you set out the trunnions of oscillating 
engines, so that they shall be at right angles with the interior 
of the cylinder ? 

A, — Having bored the cylinder, faced the flange, and bored 
out the hole through which the boring bar passes, put a piece 
of wood across the mouth of the cylinder, and jam it in, and put 
a similar piece in the hole through the bottom of the cylinder. 
Mark the centre of the cylinder upon each of these pieces, and 
put into the bore of each trunnion an iron plate, with a small 
indentation in the middle to receive the centre of a lathe, and 
adjusting screws to bring the centre into any required position. 
The cylinder must then be set in a lathe, and hung by the cen- 
tres of the trunnions, and a straight edge must be put across the 
cylinder mouth and levelled, so as to pass through the line in 
which the centre of the cylinder lies. Another similar straight 
edge, and similarly levelled, must be similarly placed across the 
cylinder bottom, so as to pass through the central line of the 
cylinder ; and the cylinder is then to be turned round in the 
trunnion centres — the straight edges remaining stationary, 
which will at once show whether the trunnions are in the same 
horizontal plane as the centre of the cylinder, and if not, the 
screws of the plates in the trunnions must be adjusted until the 
central point of the cylinder just comes to the straight edge, 
whichever end of the cylinder is presented. To ascertain 
whether the trunnions stand in a transverse plane, parallel to 
the cylinder flange, it is only necessary to measure down from 
the flange to each trunnion centre ; and if both these conditions 
are satisfied, the position of the centres may be supposed to be 



HOW TO SET THE SLIDE VALVE. 393 

riglit. The trunnion bearings are then turned, and are fitted 
into blocks of wood, in which they run while the packing space 
is being turned out. Where many oscillating engines are made, 
a lathe with four centres is used, which makes the use of straight 
edges in setting out the trunnions superfluous. 

724. Q, — Will you explain how the slide valve of a marine 
engine is set ? 

A, — Place the crank in the position corresponding to the 
end of the stroke, which can easily be done in the shop with a 
level, or plumb line ; but in a steam vessel another method be- 
comes necessary. Draw the transverse centre line, answering to 
the centre line of the crank shaft, on the sole plate of the 
engine, or on the cylinder mouth if the engine be of the direct 
action kind ; describe a circle of the diameter of the crank pin 
upon the large eye of the crank, and mark off on either side of 
the transverse centre line a distance equal to the semi-diameter 
of the crank pin. From the point thus found, stretch a line to 
the edge of the circle described on the large eye of the crank, 
and bring round the crank shaft till the crank pin touches the 
stretched line ; the crank may thus be set at either end of its 
stroke. When the crank is thus placed at the end of the stroke^ 
the valve must be adjusted so as to have the amount of lead, or 
opening on the steam side, which it is intended to give at the 
beginning of the stroke ; the eccentric must then be turned 
round upon the shaft until the notch in the eccentric rod comes 
opposite the pin on the valve lever, and falls into gear : mark 
upon the shaft the situation of the eccentric, and put on the 
catches in the usual way. The same process must be repeated 
for going astern, shifting round the eccentric to the opposite 
side of the shaft, until the rod again falls into gear. In setting 
valves, regard must of course be had to the kind of engine, the 
arrangements of the levers, and the kind of valve employed ; 
and in any general instructions it is impossible to specify every 
modification in the procedure that circumstances may render 
advisable. 

725. Q.— Is a similar method of setting the valve adopted 
when the link motion is employed. 



394 HOW TO SET THE LINK MOTION. 

A. — Each end of the link of the link motion has the kind 
of motion communicated to it that is due to the action of the 
particular eccentric with which that end is in connection. In 
that form of the link motion in which the link itself is moved 
up or down, there is a different amount of lead for each different 
position of the link, since to raise or lower the link is tanta- 
mount to turning the eccentric round on the shaft. In that 
form of the link motion in which the link itself is not raised or 
lowered, but is susceptible of a motion round a centre in the 
manner of a double ended lever, the lead continues uniform. 
In both forms of the link motion, as the stroke of the valve 
may be varied to any required extent while the lap is a constant 
quantity, the proportion of the lap relatively to the stroke of 
the valve may also be varied to any required extent, and the 
amount of the lap relatively with the stroke of the valve deter- 
mines the amount of the expansion. In setting the valve when 
fitted with the link motion, the mode of procedure is much the 
same as when it is moved by a simple eccentric. The first thing 
is to determine if the eccentric rods are of the proper length, 
and this is done by setting the valve at half stroke and turning 
round the eccentric, marking each extremity of the travel of 
the end of the rod. The valve attachment should be midway 
between these extremes; and if it is not so, it must be made so 
by lengthening or shortening the rod. The forward and back- 
ward eccentric rods are to be adjusted in this way, and this 
being done, the engine is to be put to the end of the stroke, 
and the eccentric is to be turned round until the amount of 
lead has been given that is desired. The valve must be 
tried by turning the engine round to see that it is right at both 
centres, for going ahead and also for going astern. In some 
examples of the link motion, one of the eccentric rods is 
made a little longer than the other, and the position of the 
point of suspension or point of support powerfully influences the 
action of the link in certain cases, especially if the link and 
this point are not in the same vertical line. To reconcile all 
the conditions proper to the satisfactory operation of the 
valve in the construction of the link motion, is a problem 



HOW TO MANAGE MARINE BOILERS. 395 

requiring a good deal of attention and care for its satisfactory 
solution ; and to make sure .that this result is attained, the 
engine must be turned round a sufficient number of times to 
enable us to ascertain if the valve occupies the desired position, 
both at the top and bottom centres, whether the engine is going 
ahead or astern. This should also be tried with the starting 
handle in the different notches, or, in other words, with the 
sliding block in the slot or opening of the link in different 
positions. 

MANAGEMENT OF MARINE BOILERS. 

726. Q, — You have already stated that the formation of 
salt or scale in marine boilers is to be prevented by blowing out 
into the sea at frequent intervals a portion of the concentrated 
water. Will you now explain how the proper quantity of water 
to be blown out is determined ? 

A. — By means of the salinometer, which is an instrument 
for determining the density of the water, constructed on the 
principle of the hydrometer for telling the strength of spirits. 
Some of the water is drawn off from the boiler from time to time, 
and the salinometer is immersed in it after it has been cooled. 
By the graduations of the salinometer the saltness of this water 
is at once discovered ; and if the saltness exceeds 8 ounces of 
salt in the gallon, more water should be blown out of the boiler 
to be replenished with fresher water from the sea, until the 
prescribed limit of freshness is attained. Should the sali- 
nometer be accidentally broken, a temporary one may be 
constructed of a phial weighted with a few grains of shot or 
other convenient weight. The weighted phial is first to be 
floated in fresh water, and its line of floatation marked ; then to 
be floated in salt water, and its line of floatation marked ; and 
another mark of an equal height above the salt water mark will 
be the blow off point. 

727. Q. — How often should boilers be blown off in order to 
keep them free from incrustation ? 

-4.^Flue boilers generally require to be blown off about 



396 HOW TO PREVENT INCRUSTATION. 

twice every watch, or about twice in the four hours; but 
tubular boilers may require to be blown off once every twenty 
minutes, and such an amount of blowing off should in every 
case be adopted, as will effectually prevent any injurious 
amount of incrustation. 

728. Q. — In the event of scale accumulating on the flues of 
a boiler, what is the best way of removing it ? 

A.—U the boilers require to be scaled, the best method of 
performing the operation appears to be the following :— Lay a 
train of shavings along the flues, open the safety valve to 
prevent the existence of any pressure within the boiler, and 
light the train of shavings, which, by expanding rapidly the 
metal of the flues, while the scale, from its imperfect conducting 
power, can only expand slowly, will crack off the scale; by 
washing down the flues with a hose, the scale will be carried 
to the bottom of the boiler, or issue, with the water, from the 
mud-hole doors. This method of scaling must be practised 
only by the engineer himself, and must not be intrusted to the 
firemen who, in their ignorance, might damage the boiler by 
overheating the plates. It is only where the incrustation upon 
the flues is considerable that this method of removing it need 
be practised ; in partial cases the scale may be chipped off by a 
hatched faced hammer, and the flues may then be washed down 
with the hose in the manner before described. 

729. Q. — Should the steam be let out of the boiler, after it 
has blown out the water, when the engine is stopped ? 

A. — No ; it is better to retain the steam in the boiler, as the 
heat and moisture it occasions soften any scale adhering to 
the boiler, and cause it to peel off. Care must, however, be 
taken not to form a vacuum in the boiler ; and the gauge 
cocks, if opened, will prevent this. 

730. Q. — Are tubular boilers liable to the formation of scale 
in certain places, though generally free from it ? 

A. — In tubular boilers a good deal of care is required to 
prevent the ends of the tubes next the furnace from becoming 
coated with scale. Even when the boiler is tolerably clean in 
other places the scale will collect here ; and in many cases 



HOW TO REMOVE INCRUSTATION. 397 

wliere the amount of blowing off previously found to suffice for 
flue boilers bas been adopted, an incrustation five eighths of an 
inch in thickness has formed in twelve months round the furnace 
ends of the tubes, and the stony husks enveloping them have 
actually grown together in some parts so as totally to exclude 
the water. 

731. §. — When a tubular boiler gets incrusted in the 
manner you have described, what is the best course to be 
adopted for the removal of the scale ? 

^. — When a boiler gets into this state the whole of the 
tubes must be pulled out, which may be done by a Spanish 
windlass combined with a pair of blocks ; and three men, when 
thus provided, will be able to draw out from 50 to 70 tubes 
per day, — those tubes with the thickest and firmest incrusta- 
tions being, of course, the most difficult to remove. The act 
of drawing out the tubes removes the incrustation; but the 
tubes should afterward be scraped by drawing them backward 
and forward between the old files, fixed in a vice, in the form 
of the letter V. The ends of the tube should then be heated 
and dressed with the hammer, and plunged while at a blood 
heat into a bed of sawdust to make them cool soft, so that they 
may be riveted again with facility. A few of the tubes will be 
so far damaged at the ends by the act of drawing them out, as 
to be too short for reinsertion : this result might be to a con- 
siderable extent obviated by setting the tube plates at different 
angles, so that the several horizontal rows of tubes would not 
be originally of the same length, and the damaged tubes of the 
long rows would serve to replace the short ones ; but the prac- 
tice would be attended with other inconveniences. 

732. Q. — Is there no other means of keeping boilers free 
from scale than by blowing off ? 

A. — Muriatic acid, or muriate of ammonia, commonly called 
sal-ammoniac, introduced into a boiler, prevents scale to a great 
extent ; but it is liable to corrode the boiler internally, and also 
to damage the engine, by being carried over with the steam ; 
and the use of sucl\ intermixtures does not appear to be neces- 
sary, if blowing off from the surface of the water is largely 
18 



398 HOW TO REPAIR DAMAGED BOILERS. 

practised. In old boilers, however, already incmsted with 
scale, the use of muriate of ammonia may sometimes be 
advantageous. 

733. Q. — Are not the tubes of tubular boilers liable to be 
choked up by deposits of soot ? 

A, — The soot which collects in the inside of the tubes of 
tubular boilers is removed by means of a brush, like a large 
bottle brush ; and the carbonaceous scale, which remains 
adhering to the interior of the tubes, is removed by a circular 
scraper. Ferules in the tubes interfere with the action of this 
scraper, and in the case of iron tubes ferules are now generally 
discarded ; but it will sometimes be necessary to use ferules for 
iron tubes, where the tubes have been drawn and reinserted, as 
it may be difficult to refix the tubes without such an auxiliary. 
Tubes one tenth of an inch in thickness are too thin : one eighth 
of an inch is a better thickness, and such tubes will better 
dispense with the use of ferules, and will not so soon wear into 
holes. 

734. Q, — If the furnace or flue of a boiler be injured, how 
do you proceed to repair it ? 

A. — If from any imperfection in the roof of a furnace or flue 
a patch requires to be put upon it, it will be better to let the 
patch be applied upon the upper, rather than upon the lower, 
surface of the plate ; as if applied within the furnace a recess 
will be formed for the lodgment of deposit, which will prevent 
the rapid transmission of the heat in that part ; and the iron 
will be very liable to be again burned away. A crack in a plate 
may be closed by boring holes in the direction of the crack, and 
inserting rivets with large heads, so as to cover up the imper- 
fection. If the top of the furnace be bent down, from the boiler 
having been accidentally allowed to get short of water, it may 
be set up again by a screw jack, — a fire of wood having been 
previously made beneath the injured plate ; but it will in general 
be nearly as expeditious a course to remove the plate and intro- 
duce a new one, and the result will be more satisfactory. 

735. Q. — In the case of the chimney being carried away by 
shot or otherwise, what course would you pursue ? 



MANAGEMENT OF MARINE ENGINES. 399 

A, — In some cases of collision, the funnel is carried away and 
lost overboard, and such cases are among the most diflGlcult for 
which a remedy can be sought. If flame come out of the chim- 
ney when the funnel is knocked away, so as to incur the risk 
of setting the ship on fire, the uptake of the boiler must be 
covered over with an iron plate, or be sufficiently covered to 
prevent such injury. A temporary chimney must then be made 
of such materials as are on board the ship. If there are bricks 
and clay or lime on board, a square chimney may be built with 
them, or, if there be sheet iron plates on board, a square chim- 
ney may be constructed of them. In the absence of such mate- 
rials, the awning stanchions may be set up round the chimney, 
and chain rove in through among them in the manner of wicker 
work, so as to make an iron wicker chimney, which may then 
be plastered outside with wet ashes mixed with clay, flour, or 
any other mat^ial that will give the ashes cohesion. War 
steamers should carry short spare funnels, which may easily be 
set up should the original funnel be shot away ; and if a jet of 
steam be let into the chimney, a very short and small funnel 
will suffice for the purpose of draught. 

MANAGEMENT OF MAEINE ENGINES. 

736. Q, — What are the most important of the points which 
suggest themselves to you in connection with the management 
of marine engines ? 

A, — The attendants upon engines should prepare themselves 
for any casualty that may arise, by considering possible cases 
of derangement, and deciding in what way they would act 
should certain accidents occur. The course to be pursued must 
have reference to particular engines, and no general rules can 
therefore be given ; but every marine engineer shoud be prepared 
with the measures to be pursued in the emergencies in which 
he may be called upon to act, and where everything may depend 
upon his energy and decision. 

737. Q. — What is the first point of a marine engineer's 
duty ? 



400 SAFETY OF THE BOILER. 

A, — The safe custody of the boiler. He must see that the 
feed is maintained, being neither too high nor too low, and 
that blowing out the supersalted water is practised sufficiently. 
The saltness of the water at every half hour should be entered 
in the log book, together with the pressure of steam, number of 
revolutions of the engine, and any other particulars which have 
to be recorded. The economical use of the fuel is another 
matter which should receive particular attention. If the coal 
is very small, it should be wetted before being put on the fire. 
Next to the safety of the boiler, the bearings of the engine are 
the most important consideration. These points, indeed, con- 
stitute the main parts of the duty of an engineer, supposing no 
accident to the machinery to have taken place. 

738. Q. — If the eccentric catches or hoops were disabled, 
how would you work the valve ? 

A. — If the eccentric catches or hoops break^or come off, and 
the damage cannot readily be repaired, the valve may be worked 
by attaching the end of the starting handle to any convenient 
part of the other engine, or to some part in connection with the 
connecting rod of the same engine. In side lever engines, with 
the starting bar hanging from the top of the diagonal stay, as 
is a very common arrangement, the valve might be wrought by 
leading a rope from the side lever of the other engine through 
blocks so as to give a horizontal pull to the hanging starting 
bar, and the bar could be brought back by a weight. Another 
plan would be, to lash a piece of wood to the cross tail butt of 
the damaged engine, so as to obtain a sufficient throw for 
working the valve, and then to lead a piece of wood or iron, 
from a suitable point in the piece of wood attached to the cross 
tail, to the starting handle, whereby the valve would receive its 
proper motion. In oscillating engines it is easy to give the 
required motion to the valve, by deriving it from the oscillation 
of the cylinder. 

739. Q. — What would you do if a crank pin broke ? 

A. — ^If the crank pin breaks in a paddle vessel with two 
engines, the other engine must be made to work one wheel. 
In a screw vessel the same course may be pursued, provided 



ENGINEER TO PROVIDE FOR VARIOUS ACCIDENTS. 401 

the broken crank is not the one through which the force of the 
other engine is communicated to the screw. In such a case the 
vessel will be as much disabled as if she broke the screw shaft 
or screw. 

740. Q, — Will the unbroken engine, in the case of disarrange- 
ment of one of the two engines of a screw or paddle vessel, be 
able of itself to turn the centre ? 

A. — It will sometimes happen, when there is much lead 
upon the slide valve, that the single engine, on being started, 
cannot be got to turn the centre if there be a strong opposing 
wind and sea ; the piston going up to near the end of the stroke, 
and then coming down again without the crank being able to 
turn the centre. In such cases, it will be necessary to turn the 
vessel's head sufficiently from the wind to enable some sail to 
be set ; and if once there is weigh got upon the vessel the 
engine will begin to work properly, and will continue to do so 
though the vessel be put head to wind as before. 

741. Q. — ^What should be done if a crack shows itself in any 
of the shafts or cranks ? 

A, — If the shafts or cranks crack, the engine may neverthe- 
less be worked with moderate pressure to bring the vessel into 
port ; but if the crack be very bad, it will be expedient to fit 
strong blocks of wood under the ends of the side levers, or 
other suitable part, to prevent the cylinder bottom or cover 
from being knocked out, should the damaged part give way. 
The same remark is applicable when flaws are discovered in 
any of the main parts of the engine, whether they be malleable 
or cast iron ; but they must be carefully watched, so that the 
engines may be stopped if the crack is extending further. 
Should fracture occur, the first thing obviously to be done is 
to throw the engines out of gear ; and should there be much 
weigh on the vessel, the steam should at once be thrown on 
the reverse side of the piston, so as to counteract the pressure 
of the paddle wheel. 

742. Q. — Have you any information to offer relative to the 
lubrication of engine bearings ? 

A, — A very useful species of oil cup is now employed in a 



402 THE HEATING OF BEARINGS. 

number of steam vessels, and which, it is said, accomplishes a 
considerable saving of oil, at the same time that it Qiore effect- 
ually lubricates the bearings. A ratchet wheel is fixed upon a 
little shaft which passes through the side of the oil cup, and is 
put into slow revolution by a pendulum attached to its outside, 
and in revolving it lifts up little buckets of oil and empties them 
down a funnel upon the centre of the bearing. Instead of 
buckets a few short pieces of wire are sometimes hung on the 
internal revolving wheel, the drops of oil which adhere on 
rising from the liquid being deposited upon a high part set 
upon the funnel, and which, in their revolution, the hanging 
wires touch. By this plan, however, the oil is not well supplied 
at slow speeds, as the drops fall before the wires are in proper 
position for feeding the journal. Another lubricator consists 
of a cock or plug inserted in the neck of the oil cup, and set in 
revolution by a pendulum and ratchet wheel, or any other 
means. There is a small cavity in one side of the plug, which 
is filled with oil when that side is uppermost, and delivers the 
oil through the bottom pipe when it comes opposite to it. 

743. Q. — Wliat are the prevailing causes of the heating of 
bearings ? 

A. — Bad fitting, deficient surface, and too tight screwing 
down. Sometimes the oil hole will choke, or the syphon wick 
for conducting the oil from the oil cup into the central pipe 
leading to the bearing will become clogged with mucilage from 
the oil. In some cases bearings heat from the existence of a 
cruciform groove on the top brass for the distribution of the oil, 
the effect of which is to leave the top of the bearings dry. In 
the case of revolving journals the plan for cutting a cruciform 
channel for the distribution of the oil does not do much damage ; 
but in other cases, as in beam journals, for instance, it is most 
injurious, and the brasses cannot wear well wherever the plan 
is pursued. The right way is to make a horizontal groove along 
the brass where it meets the upper surface of the bearing, so 
that the oil may be all deposited on the highest point of the 
journal, leaving the force of gravity to send it downward. 
This channel should, of course, stop short a small distance from 



DUTIES OF A LOCOMOTIVE DEIVEE. 403 

each flange of the brass, otherwise the oil would run out at the 
ends. 

744. Q. — If a bearing heats, what is to be done ? 

A, — The first thing is to relax the screws, slow or stop the en- 
gine, and cool the bearing with water, and if it is very hot, then 
hot water may be first employed to cool it, and then cold. Oil 
with sulphur intermingled is then to be administered, and as the 
parts cool down, the screws may be again cautiously tightened, 
so as to take any jump off the engine from the bearing being 
too slack. The bearings of direct acting screw engines require 
constant watching, as, if there be any disposition to heat mani- 
fested by them, they will probably heat with great rapidity 
from the high velocity at which the engines work. Every bear- 
ing of a direct acting screw engine should have a cock of water 
laid on to it, which may be immediately opened wide should 
heating occur ; and it is advisable to work the engine constantly, 
partly with water, and partly with oil applied to the bearings. 
The water and oil are mixed by the friction into a species of 
soap which both cools and lubricates, and less oil moreover is 
used than if water were not employed. It is proper to turn off 
the water some time before the engine is stopped, so as to 
prevent the rusting of the bearings. 

MANAGEMENT OF LOCOMOTIVES. 

745. Q. — What are the chief duties of the engine driver of a 
locomotive ? 

A. — His first duties are those which concern the safety of 
the train ; his next those which concern the safety and right 
management of the engine and boiler. The engine driver's 
first solicitude should be relative to the observation and right 
interpretation of the signals ; and it is only after these demands 
upon his attention have been satisfied, that he can look to the 
state of his engine. 

746. Q. — As regards the engine and boiler, what should his 
main duties be ? 

A, — The engineer of a locomotive should constantly be upon 
the foot board of the engine, so that the regulator, the whistle. 



404 MANAGEMENT OF THE BOILEE. 

or the reversing handle may be used instantly, if necessary ; he 
must see that the level of the water in the boiler is duly main- 
tained, and that the steam is kept at a uniform pressure. In 
feeding the boilers with water, and the furnaces with fuel, a 
good deal of care and some tact are necessary, as irregularity in 
the production of steam will often occasion priming, even though 
the water be maintained at a uniform level ; and an excess 
of water will of itself occasion priming, while a deficiency is 
a source of obvious danger. The engine is generally furnished 
with three gauge cocks, and water should always come out of 
the second gauge cock, and steam out of the top one when the 
engine is running : but when the engine is at rest, the water in 
the boiler is lower than when in motion, so that when the 
engine is at rest, the water will be high enough if it just reaches 
to the middle gauge cock. In all boilers which generate steam 
rapidly, the volume of the water is increased by the mingled 
steam, and in feeding with cold water the level at first falls ; but 
it rises on opening the safety valve, which causes the steam in the 
water to swell to a larger volume. In locomotive boilers, the 
rise of the water level due to the rapid generation of steam is 
termed " false water." To economize fuel, the variable expan- 
sion gear, if the engine has one, should be adjusted to the load, 
and the blast pipe should be worked with the least possible 
contraction ; and at stations the damper should be closed to 
prevent the dissipation of heat. 

747. Q.—ln starting from a station, what precautions should 
be observed with respect to the feed ? 

A. — In starting from a station, and also in ascending inclined 
planes, the feed water is generally shut off; and therefore before 
stopping or ascending inclined planes, the boiler should be well 
filled up with water. In descending inclined planes an extra 
supply of water may be introduced into the boiler, and the fire 
may be fed, as there is at such times a superfluity of steam. In 
descending inclined planes the regulator must be partially closed, 
and it should be entirely closed if the plane be very steep. The 
same precaution should be observed in the case of curves, or rough 
places on the line, and in passing over points or crossings. 



MAKAGEMENT OF THE FEED PUMPS. 405 

748. Q, — In approaching a station, how should the supply of 
water and fael be regulated ? 

A. — The boiler should be well filled with water on approach- 
ing a station, as there is then steam to spare, and additional 
water cannot be conveniently supplied when the engine is 
stationary. The furnace should be fed with small quantities 
of fuel at a time, and the feed should be turned off just 
before a fresh supply of fuel is introduced. The regulator 
may, at the same time, be partially closed; and if the blast 
pipe be a variable one, it will be expedient to open it 
widely while the fuel is being introduced, to check the rush 
of air in through the furnace door, and then to contract it very 
much so soon as the furnace door is closed, in order to recover 
the fire quickly. The proper thickness of coke upon the grate 
depends upon the intensity of the draught; but in heavily 
loaded engines it is usually kept up to the bottom of the fire 
door. Care, however, must be taken that the coke does not 
reach up to the bottom row of tubes so as to choke them up. 
The fuel is usually disposed on the grate like a vault ; and if the 
fire box be a square one, it is heaped high in the corners, the 
better to maintain the combustion. 

749. Q^ — How can you tell whether the feed pumps are 
operating properly ? 

A. — To ascertain whether the pumps are acting well, the pet 
cock must be turned, and if any of the valves stick they will 
sometimes be induced to act again by working with the pet 
cock open, or alternately open and shut. Should the defect 
arise from a leakage of steam into the pump, which prevents 
the pump from drawing, the pet cock remedies the evil by 
permitting the steam to escape. 

750. Q. — What precautions should be taken against priming 
in locomotives ? 

A. — Should priming occur from the water in the boiler 
being dirty, a portion of it may be blown out; and should 
there be much boiling down through the glass gauge tube, the 
stop cock may be partially closed. The water should be 
wholly blown out of locomotive boilers three times a week. 



406 PEECAUTIONS IN STOPPING THE TEAIN. 

and at those times two mud-hole doors at opposite comers 
of the boiler should be opened, and the boiler be washed inter- 
nally by means of a hose. If the boiler be habitually fed with 
dirty water, the priming will be a constant source of trouble. 

751. Q. — What measures should the locomotive engineer 
take, to check the velocity of the train, on approaching a station 
where he has to stop ? 

A, — On approaching a station the regulator should be 
gradually closed, and it should be completely shut about half a 
mile from the station if the train be a very heavy one : the train 
may then be brought to rest by means of the breaks. Too 
much reliance, however, must not be put upon the breaks, 
as they sometimes give way, and in frosty weather are nearly 
inoperative. In cases of urgency the steam may be thrown 
upon the reverse side of the piston, but it is desirable to obviate 
this necessity as far as possible. At terminal stations the steam 
should be shut off earlier than at roadside stations, as a collision 
will take place at terminal stations if the train overshoots the 
place where it ought to stop. There should always be a good 
supply of water when the engine stops, but the fire may be 
suffered gradually to burn low toward the conclusion of the 
journey. 

752. Q. — What is the duty of an engine man on arriving at 
the end of his journey ? 

A, — So soon as the engine stops it should be wiped down, 
and be then carefully examined : the brasses should be tried, 
to see whether they are slack or have been heating ; and, by the 
application of a gauge, it should be ascertained occasionally 
whether the wheels are square on their axles, and whether the 
axles have end play, which should be prevented. The stuffing 
boxes must be tightened, and the valve gear examined, and the 
eccentrics be occasionally looked at to see that they have not 
shifted on their axles, though this defect will be generally inti- 
mated by the irregular beating of the engines. The tubes 
should also be examined and cleaned out, and the ashes 
emptied out of the smoke box through the small ash door 
at the end. If the engine be a six-wheeled one, with the driv- 



WHAT TO DO IF A TUBE BUKSTS. 407 

ing wheels in the middle, it will be liable to pitch and oscillate 
if too much weight be thrown upon the driving wheels ; and 
where such faults are found to exist, the weight upon the driv- 
ings wheels should be diminished. The practice of blowing 
off the boiler by the steam, as is always done in marine boilers, 
should not be permitted as a general rule in locomotive boilers, 
when the tubes are of brass and the fire box of copper ; but 
when the tubes and fire boxes are of iron, there will not be an 
equal risk of injury. Before starting on a journey, the engine 
man should take a summary glance beneath the engine — but 
before doing so he ought to assure himself that no other engine 
is coming up at the time. The regulator, when the engine is 
standing, should be closed and locked, and the eccentric rod 
be fixed out of gear, and the tender break screwed down ; the 
cocks of the oil vessels should at the same time be shut, but 
should all be opened a short time before the train starts. 

753. Q. — What should be done if a tube bursts in the boiler ? 
A. — When a tube bursts, a wooden or iron plug must be 

driven into each end of it, and if the water or steam be rushing 
out so fiercely that the exact position of the imperfection cannot 
be discovered, it will be advisable to diminish the. pressure by 
increasing the supply of feed water. Should the leak be so 
great that the level of the water in the boiler cannot be main- 
tained, it will be expedient to drop the bars and quench the fire, 
so as to preserve the tubes and fire box from injury. 

754. Q. — If any of the working parts of a locomotive break 
or become deranged, what should be done ? 

A. — Should the piston rod or connecting rod break, or the 
cutters fall out or be clipped off — as sometimes happens to the 
piston cutter when the engine is suddenly reversed upon a 
heavy train — the parts should be disconnected, if the connection 
cannot be restored, so as to enable one engine to work ; and of 
course the valve of the faulty engine must be kept closed. If 
one engine has not power enough to enable the train to proceed 
with the blast pipe full open, the engine may perhaps be able 
to take on a part of the carriages, or it may run on by itself to 
fetch assistance. The same course must be pursued if any of 



408 AN engine-driver's duties. 

the valve gearing becomes deranged, and tlie defects cannot 
be rectified upon the spot. 

755. Q. — What are the most usual causes of railway collisions ? 
A, — Probably fogs and inexactness in the time kept by the 

trains. Collisions have sometimes occurred from carriages having 
been blown from a siding on to the rails by a high wind ; and 
the slippery state of the rails, or the fracture of a break, has 
sometimes occasioned collisions at terminal stations. Collision 
has also repeatedly taken place from one engine having over- 
taken another, from the failure of a tube in the first engine, or 
from some other slight disarrangement ; and collision has also 
taken place from the switches having been accidentally so left 
as to direct the train into a siding, instead of continuing it on 
the main line. Every train now carries fog signals, which are 
detonating packets, which are fixed upon the rails in advance 
or in the rear of a train which, whether from getting off the 
rails or otherwise, is stopped upon the line, and which are 
exploded by the wheels of any approaching train. 

756. Q. — What other duties of an engine-driver are there 
deserving attention ? 

A. — They are too various to be all enumerated here, and they 
also vary somewhat with the nature of the service. One rule, 
however, of universal application, is for the driver to look after 
matters himself, and not delegate to the stoker the duties 
which the person in charge of the engine should properly per- 
form. Before leaving a station, the engine-driver should assure 
himself that he has the requisite supply of coke and water. 
Besides the firing tools and rakes for clearing the tubes, he 
should have with him in the tender a set of signal lamps and 
torches, for tunnels and for night, detonating signals, screw 
keys, a small tank of oil, a small cask of tallow, and a small 
box of waste, a coal hammer, a chipping hammer, some wooden 
and iron plugs for the tubes, and an iron tube holder for insert- 
ing them, one or two buckets, a screw jack, wooden and iron 
wedges, split wire for pins, spare cutters, some chisels and files, 
a pinch bar, oil cans and an oil syringe, a chain, some spare 
bolts, and some cord, spun yam, and rope. 




1 1^ D E X . 



Accidents in steam vessels, proper 
preparation for, 400. 

Admiralty rule for horse power, 107. 

Adhesion of wheels of locomotives to 
rails, 249. 

Air, velocity of, entering a vacuum, 6 ; 
required for combustion of coal, 74 ; 
law of expansion of, bj'' heat, 85. 

Air pump, description of, 49 ; action of, 
51, 58, 59 , proper dimensions of, 158. 

Air pump of marine engines, details of, 
226. 

Air pump of oscillating engine, 310. 

Air pump of direct acting screw en- 
gines, 325,329. 

Air pumps made both single and dou- 
ble acting, 159 ; difference of, explain- 
ed, 159. 

Air pumps, double acting valves of, 229 ; 
bad vacuum in, 231 ; causes and rem- 
edy, 232, 233. 

Air pump rods, brass or copper, in ma- 
rine engines, 226. 

Air pump bucket, valves of, 227, 228. 

Air pump, connecting rod and cross 
liead of oscillating engine, 315. 

Air pump rod of oscillating engine, 314. 

Air pump arm, 328. 

Air vessels applied to suction side of 
pumps, 164, 165. 

"Alma," engine of, by Messrs. John 
Baurne «& Co., 323. 

" Amphion," engines of, 216. 

Amoskeag steam fire engine, 365. 

Angle iron in boilers, precautions re- 
specting, 179. 

Apparatus for raising screw propeller, 
241. 

Atmospheric valve, 36. 

Atraospneric resistance to railway 
trains, 250-25^. 



Auxiliary power, screw vessels with, 
303, 304. 

Axle bearings of locomotives, 260. 

Axle guards, 336. 

Axles and wheels of modern locomo- 
tives, 336. 

" Azof," slide valve of, 223. 

Babbitt's metal, how to compound, 
387. 

Balance piston to take pressure off slide 
valve, 326, 

Ball valves, 264. 

Barrel of boiler of modern locomotives, 
334. 

Beam, working of land engine, 46; 
main or working strength proper for, 
168. 

Bearings of engines or other machinery, 
rule for determining proper surface of, 
23. 

Bearings, heating of, how to prevent or 
remedy, 403 ; journals should always 
bottom, as, if they grip on the sides, 
the pressure is infinite. 

Beattie's screw, 299. 

Belidor's valves might be used for foot 
and delivery valves, 227. 

Bell-metal, composition of, 388. 

Blast pipe of locomotives, description 
of, 66. 

Blast in locomotives, exhaustion pro- 
duced by, 134 ; proper construction 
of the blast pipe, 134, 135 ; the blast 
pipe should be sot below the root of 
the chimney so much that the cone of 
escaping steam shall just fill the 
chimney. 

Bhist pipe with variable orifice, at one 
time much used, 136. 

Blow-oft* cock of locomotivei, 203. 



410 



INDEX. 



Blow-off cocks of marine boilers, prop- 
er construction of, 235. 

Blow-otf cocks, description of, 59. 

Blowing ofl' supersalted water from 
marine boilers, 5. 

Blowing off, estimate of heat lost by, 
191 ; mode of, 192, 396. 

Blow through valve, description of, 59. 

Blowing furnaces, power necessary for, 
377. 

Bodies, falling, laws of, 6, 7. 

Bodmer, expansion valve by, 100. 

Boilers, general description of : the 
wagon boiler, 34; the Cornish boil- 
er, 38 ; the marine flue boiler, 38 ; the 
marine tubular boiler. 40; locomotive 
boiler — see Locomotives. 

Boilers proportions of: heating surface 
of, 122-124 , fire grate, surface of, 123 ; 
consumption of fuel on each square 
foot of fire bars in wagon, Cornish, 
and locomotive boilers, 124 ; calorim- 
meter and vent of boilers, 124 ; com- 
parison of proportions of wagon, 
flue, and tubular boilers, 125-129 ; 
evaporative power of boilers, 130; 
power generated by evaporation of a 
cubic foot of water, 131 , proper pro- 
portions of modern marine boilers, 
both flue and tubular, 132 ; modern 
locomotive boilers, 133 , exhaustion 
produced by blast in locomotives, 134 ; 
increased evaporation from increased 
exliaustion, 135 ; strength of boilers, 
145 ; experiments on, by Franklin In- 
stitute, 145 ; by Mr. Fairbairn, 146 ; 
mode of commuting streneth of boil- 
er?, 146, 147 ; ^staying of, 148, 149. 

Boiler?, marine, prevented from salting 
by blowing ofl', 5 ; early locomotive 
and contemporaneous marine boilers 
compirod, 137, 138 ; chimnej^s of 
land, 134-138 ; rules for proportions of 
chimneys, 139 ; chimneys of marine 
boilers, 140. 

Boilers, constructive details of : riveting 
and caulkiuGT of land boilers, 178 ; 
proving of, 178 ; seams payed with 
mixture of whiting and linseed oil, 
178 ; setting of wagon boiler?, 178 ; 
riveting of marine boilers, 179 ; pre- 
cautions respecting angle iron, 179; 
how to punch the rivet holes and 
shear edges of plate?, 180 ; settincr of 
marine boilers in wooden vessels, 180 ; 
mastic cement for setting marine 
boilers, 180 ; composition of mastic 
cement, 181 ; best length of furnace, 
181 ; confisruration of furnace barn, 
182 ; advantages and construction of 
furnace bridges, 182 ; various forma 
of damper?, 183 ; precaulio-is against 
injury to boilers from intense heat, 
184; tubing of boilers, 185 ; proper 
moae of staying tube plates, 185 , 



proper mode of constructing steam- 
boat chimnej^s, 186 ; waste steam- 
pipe and funnel casing, 187 : tele- 
scope chimneys, 187 ; tormation of 
scale in marine boilers, 188 ; injury 
of such incrustations, 189 ; amount 
of salt in sea water, 189 ; saltness per- 
missible in boilers, 190 : amount of 
heat lost by blowing off, 191 ; mode 
of discharging the supersalted water, 
192 ; Lamb's scale preventer, 193 , in- 
ternal corrosion of marine boilers, 
194 ; causes of internal corrosion, 195 ; 
surcharged steam produced from salt 
water, 196 ; stop valves between boil- 
ers, 197 ; safety or escape valve on 
feed pipe, 198 ; locomotive boilers 
consist of the fire box, barrel for 
holding tubes, and smoke box, 199 ; 
dimensions of the barrel and thick- 
ness of plates, 199 ; mode of staying 
fire box and furnace crown, 200 ; firo 
bars, ash box, and chimney, 201 ; 
steam dome used only in old engines, 
202 ; manhole, mudholes, and blow-oft" 
cock, 202, 203 ; tube plate, and modo 
of securing tubes, 204 ; expanding 
mandrels, 204 ; various forms of regu- 
lator, 205. 

Boilers of modern locomotives, 334. 

Boiler, the, proper care of, the first du- 
ty of tLe engineer, 400. 

Bolts, proper proportions of, 247. 

Boring of cylinders, 380. 

Boulton and Watt's rules for fly wheel, 
9 ; proportions of marine flue boilers, 
123 ; rule for proportions of chimneys 
of land boilers, 139 ; of marine boilers, 
140 ; experiments on the resistance 
of vessels in water, 273-276. 

Bourdon's steam and vacuum gauges, 
111, 340. 

Bourne, expansion valves by, 100, 101. 

Bourne, Messrs. J. & Co., direct act' 
ing screw engines by, 323. 

Brass for bearing?, composition of, 387. 

Brazing solders, 388. 

Bridges in furnaces, benefits of, 182. 

Burning of boilers, precautions against, 
184. 

Bursting velocity of fly wheel, 10 ; and 
of railway wheel?, 11. 

Bursting of boiler?, 149 ; causes of, 150 ; 
precautions against, 151 ,* may be 
caused by accumulations of salt, 152. 

Butterfly valves of air pump, 227. 

Cabrcy, expansion valve by^ 100. 

Calorimeter of boilers, definition of, 124. 

Cams, proper forms of, 98. 

Cast iron, i^trei'gth of, 25-27; proper^ 
tion? of cast inm beam.s, 28 ; effects 
of d'fferent kinds of strams on beams, 
29-31; strength to resist shocks not 
proportional to strength to resist 



INDEX. 



411 



strains, 34 ; to attain maximum 
strength should "be combined with 
wrought iron, 35. 

Casting of cylinders, 378, 379. 

Case-hardeuing, how to accomplish, 
385. 

Cataract, explanation of nature and 
uses of, 119, 120. 

Caulking of land boilers, 178. 

Cement, mastic, for eetting marine 
boilers, 180. 

Central forces, 9. 

Centre of pressure of paddle wheels, 
279. 

Centres of gravity, gyration and oscil- 
lation, 11. 

Centres for fixing arms of paddle 
wheel, 242. 

Centres of an engine, how to lay off, 
390, 

Centrifugal force, nature of, 9 ; rule for 
determining, 10 ; bursting velocity 
of fly wheel, 10, 11; and of railway 
wheels, 11. 

Centrifugal pump will supersede com- 
mon pump, 213. 

Centripetal force, nature of, 9. 

Chimney of locomotives, 201. 

Chimney of steam vessels, what to do 
if carried away, 399. 

Chimneys of land boilers, 134, 138 ; 
Boulton and Watt's rule for propor- 
tions of, 139 ; of marine boilers, 140. 

Chimneys, exhaustion produced by, 
134, 138 ; high and wide chimneys in 
locomotives injurious, 135. 

Chimneys of steamboats, 186; tele- 
scope, 187. 

Clark's patent steam tire regulator, 
340. 

Coal, constituents of, 74 ; combustion 
of air required for, 74 ; evaporative 
efficacy of, 72 ; of wood, turf, and 
coke, 76. 

Cocks, proper construction of, 234-237. 

Cog wheels for screw engines, 63. 

Coke, evaporative efficacy of, 76. 

Cold water pump, description of, 50 ; 
rule for size of, 165. 

Combustion, nature of, 73. 

Combustion of coal, air required for, 
74. 

Combustion, slow and rapid, compara- 
tive merits of, 77 ; rapid combustion 
necessary in steam vessels, and ena- 
bles less heating surface in the boil- 
er to suffice, 77. 

Conchoidal propeller, 333. 

Condensation of steam, water required 
for, 160, 161. 

Condenser, description of, 49 ; action 
of, 50, 59 ; proper dimensions of, 158. 

Condenser of oscillating engine, 311. 

Condenser of direct acting screw en- 
gine, 324. 



Condensing engine, definition of, 1. 
Condensing water, how^ to provide 

when deficient, 208. 
Conical pendulum or governor, 16. 
Connecting rod, description of, 46, 47 ; 

strength proper for, 167, 171. 
Connecting rod of direct acting screw 

engines, 327 ; of locomotives, 259. 
Consumption of fuel on each square 

foot of fire bars in wagon, Cornish, 

and locomotive boilers, 123. 
Copper, strength of, 26. 
Corliss's steam engine, 354-357. 
Corrosion produced by surcharged 

steam, 196. 
Corrosion of marine boilers, 194 ; causes 

of, 195. 
Cost of locomotives, 249. 
Cotton spinning, power necessary for, 

376. 
Counter for counting strokes of an 

engine, 116. 
Crank, description of, 46 ; unequal 

leverage of, corrected by flywheel, 2 ; 

no power lost by, 17 ; action of, 54 ; 

strength proper for, 172, 173. 
Crank of direct acting screw engines, 

324, 329, 330. 
Crank pin, strength proper for, 173. 
Crank pin of direct acting screw en- 
gines, 329. 
Cranked axle of locomotive?, 259. 
Cross head, description of, 58 ; strength 

proper for, 174. 
Cross head of direct acting screw en- 
gines, 328. 
Cross tail, description of, 59. 
Cylinder, description of, 46 ; strength 

proper for, 166. 
Cylinder of oscillating engine, 309, 311, 

321 ; of direct acting screw engine, 

824, 325. 
Cylinders should have a steam jacket, 

and be felted and planted, 218 ; 

should have escape valves, 219. 
Cylinders of locomotives should be 

large, 254; proper arrangement of, 

257. 
Cylinders, how to cast, 378, 379 ; how to 

bore, 380 ; how to grind, 381. 
Cylinder jacket, advantages of, 91. 

Damper, 37. 

Dampers, various forms of, 183. 
Dead wood, hole in, for screw, 239. 
Delivery valve, description of, 50. 
Delivery or discharge valves, proper 

dimensions of, 160. 
Delivery valves might be made on Bel- 

idor'splan, 227. 
Delivery valves in mouth of air pump, 

227 ; of India rubber, 228-231. 
Direct acting screw engines should be 

balanced, 217. 
Direct acting screw engine by Mesirs. 



412 



INDEX. 



John Bourne & Co., 323; cylinder, 
324, 325 ; discs, 324, 329, 330 ; guides, 
325 ; screw shaft brasses, 325 ; air 
pump, 325, 320; slide valve, 326; 
balance piston, 326 ; connecting rod, 
327 ; piston rods, 327 ; cross head, 328 ; 
air pump arm, 328 ; feed pump, 328 , 
crank pin, 329 • screw shaft, 331 ; 
thrust pluramer block, 331, 332 ; link 
motion, 332 ; screw propeller, 333. 

Discharge valves, 236. 

Disc valves of India rubber for air 
pumps, 229, 230. 

Discs of direct acting screw engine in- 
stead of crank, 324, 329, 330. 

Dodds, expansion valve by, 100. 

Double acting engines, definition of, 
2,3. 

Double acting air pumps, 159 ; valves 
of, 229 ; faults of, 231, 233. 

Draw bolt, 336. 

Dredging earth out of rivers, power 
• necessary for, 377. 

Driving wheels of locomotives, 266. 

Driving piles, power necessary for, 
377. 

Duplex pump, "Worthington's, 346. 

Dundonald, Earl of, screw by, 297. 

Duty of engines and boilers, 108 ; how 
the duty is ascertainable, 109. 

Dynamometer, description of, 117. 

Dynamometric power of screw vessels, 
293. 

Eccentric, description of, 59 ; some- 
times made loose for backing, 225. 

Eccentric and eccentric rod of oscilla- 
ting engine, 316. 

Eccentric notch should be fitted with a 
brass bush, 226. 

Eccentric straps of locomotives, 261 ; 
rods of locomotives, 261. 

Eccentrics of locomotives, 260 ; how to 
readjust, 263. 

Economy of fuel in steam vessels, 307. 

Edwards, expansion valve by, 22. 

Elasticity, limits of, 27. 

Engine, high pressure, definition of, 1 ; 
low pressure, definition of, 1. 

Engines, classification of, 2; rotative, 
definition of, 2 ; rotatorj^, definition 
of, 2 ; single acting, definition of, 2 ; 
double acting, definition of, 2, 3 ; 
mode of erecting in a vessel, 244-246 ; 
how to reflx if they have becomo 
loose, 247. 

Engineers of steam vessels should 
make proper preparation for acci- 
dojils, 400. 

Equilibrium slide valve, 222-224 ; grid- 
iron valve, 224. 

Erectmg engines in a vessel, 243-246. 

Erection of engines in the workshop, 
388. 

Escape valve on feed pipe, 198. 



Escape valves for letting water out of 
cylinders, 219. 

Evaporative eflS-cacy of coal, 75 ; of 
wood, turf, and coke, 76. 

Evaporative power of boilers, 127, 130 ; 
power generated by evaporation of a 
cubic foot of water, 131 ; increase of 
evaporation due to increased exhaus- 
tion in locomotives, 135. 

Excavator, Otis' s, 372. 

Exhaustion produced by chimneys, 134, 
139 , by the blast in locomotives, 134 : 
increased evaporation from increased 
exhaustion, 135. 

Expanding mandrels for tubing boilers, 
204. 

Expansion of air by heat, 85. 

Expansion of surcharged steam by heat, 
85. 

Expansion of steam, 87 ; pressure of 
steam inversely as the space occupi- 
ed, 88 ; law of expansion, 89 ; rule 
for computing the increase of eflici- 
ency produced by working expansive- 
ly, 90 ; necessity of efficient provis- 
ions against refrigeration in working 
expansively, 91 ; advantages of steam 
jacket, 91. Forms of apparatus for 
working expansively : lap on the 
slide valve, 93 ; wire drawing the 
steam, 95 ; Cornish expansion valve, 
96 ; in rotative engines worked by a 
cam, 97 ; mode of varying the degree 
of expansion, 98 ; proper forms of 
cams, 98 ; the link motion, 99 ; expan- 
sion valves, bv Cabrey, ^Fenton, 
Dodds, Farcot, Edwards, LavagriaL:, 
Bodmer, Meyer, Hawthorn, Gonzen- 
bach, and Bourne, 99-101, 354-361. 

Expansion joint in valve casing, 219. 

Expansion valves, Cornish, 96 ; the 
link motion, 99- by Cabrey, Fenton, 
Dodds, Farcot, Edwards, Lavagrian, 
Bodmer, Meyer, Hawthorn, Gonzeu- 
bach, and Bourne, 99-101, 354-361. 

Explosions of boilers, 149; causes of 
explosions, 150 ; precautions against, 
151, 152 ; dangers of accumulation* 
of salt, 152. 

Face plates or planometers, 383. 

Falling bodies, laws of, 7. 

Farcot, expansion valve by, 100. 

Feathering paddle wheels, description 
of, 62 ; details of, 819. 

Feed pump, description of, 49 ; action 
of, 51 : proper dimensions of, 86; rul© 
for proportioning, 163. 

Feed pump plunger, 234; and valves, 
234. 

Feed pumps of locomotives, details of, 
264. 

Feed pumps of direct acting screw en- 
gines, 328. 

Fenton, expansion valve by, 100. 



INDEX. 



413 



Fire bars of locomotives, 201. 

Fire box of locomotives, mode of stay- 
ing, 200, 

Fire box of modern locomotives, 334. 

Fire engines, cost of running, 370. 

Fire grate surface of boilers, 123. 

Fire grate in locomotives should be of 
small area, 110; coke proper to be 
burned per hour on each square foot 
of bars, 110. 

Firing furnaces, proper mode of, 76. 

Flaws in valves or cylinders, how to 
remedy, 383. 

Float for regulating water level in boil- 
ers, 36, 119. 

Floats of paddle, 243. 

Floats of paddle wheels, increased re- 
sistance of, if oblique, 282; floats 
should be large, 284. 

Fly wheel corrects unequal leverage of 
crank, 3 ; proper energy for, 8 , Boul- 
ton and Watt's rule for, 9 ; bursting 
velocity of, 10; description of, 46; 
action of, in redressing irregularities 
of motion, 54. 

Foot valve, description of, 49 ; proper 
dimensions of, 160. 

Foot valves might be made on Belidor's 
plan, 227; of India rubber, 228-231. 

Frame at stern for holding screw pro- 
peller, 240. 

Framing of locomotives, 253. 

Framing of oscillating engine, 309. 

Franklin Institute, experiments on 
steam by, 83, 

French Academy, experiments on 
steam by, 83. 

Friction, nature of, 20; does not vary 
as the rubbing surfaces, but as the 
retaining pressure, 20 ; does not in- 
crease with the velocity per unit of 
distance, but increases with the ve- 
locity per unit of time, 20 ; measures 
of friction, 21 ; effect of unguents, 
21 ; kind of unguent should vary 
with the pressure, 22; Morin's ex- 
periments, 22 ; rule for determining 
proper surfaces of bearings, 23 ; fric- 
tion of rough surfaces, 24. 

Friction of the water the main cause of 
the resistance of vessels of good shape, 
272. 

Fuel burnt on each square foot of fire 
bars in wagon, Cornish, and loco- 
motive boilers, 123 ; economy of, in 
steam vessels, 307. 

Funnel casing, 187. 

Funnel, what to do if carried away, 399. 

Funnels of steam boats. See Chimneys. 

Furnaces, proper mode of firing, 76 ; 
smoke burning: Williams's argand, 
79 ; Prideaux's, 79 ; Boulton and 
Watt's dead plate, 80 ; revolving 
grate, 80; Juckes's, 81; Maudslay's, 
81; Hall's, Coupland's, Godson's, 



Robinson's, Stevens's, Hazeldine's, 
&c., 84. 

Furnaces of marine boilers, proper 
length of, 181. 

Furnace bridges, benefits of, 183. 

Fusible metal plugs useless as anti- 
dotes to explosions, 152. 

Gauges, vacuum, 4; steam, 4; gauge 

cocks and glass tubes for showing 

level of water in boiler, description 

of, 5, HI, 340. 
Gauge cocks for showing level of water 

in boiler, 5, 118, 237. 
Gearing for screw engines, 63. 
Gibs and cutters, strengths proper for, 

175. 
Giftard's injector, 347. 
Glass tubes for showing water level in 

boilers, 5, 118. 
Glass tube cocks, 237. 
Gonzenbach, expansion valve by, 101. 
Gooch's indicator, 115, 116. 
Gooch's locomotive, 68, 334. 
Governor or conical pendulum, 16, 17 ; 

description of, 47. 
Governor, Porter's patent, 342. 
Gravity, centre of, 12. 
" Great Western," boilers of, by Messrs. 

Maudslay, 122. 
Gridiron valve, 224. 
Griffith's screw, 298. 
Grinding corn, power necessary for, 

373-375. 
Grinding of cylinders, 381. 
Gudgeons, strength proper for, 163. 
Guides of locomotives, 258. 
Guides of direct acting screw engine, 

324. 
Gun metal, strength of, 26. 
Gyration, centre of, 12. 

Harvey and West's pump valves, 211. 
Hawthorn, expansion valve by, 101. 
Heat, latent, definition of, 71. 
Heat, specific, definition of, 73. 
Ileat, Regnault's experiments on, 72. 
Heat, loss of, by blowing off marine 

boilers, 191. 
Heating surface of boilers, 122. 
Heating surface per square foot of fire 

bars in locomotives, 110 ; a cubic foot 

of water evaporates by five square feet 

of heating surface, 110. 
Heating of bearings, causes of, 402 ; 

bearings should always be slack at 

the sides, else the pressure is infinite. 
High pressure engine, definition of, 1. 
High pressure engines, power of, 126. 
High speed engines, 106 , arrangements 

proper for high speeds, 106. 
Hoadley's portable engine, 351. 
Hodgson's screw, 297. 
Hoe & Co.'s steam engine, 353. 



414 



INDEX. 



Holdlnf^ down bolts of marine engines, 
or bolts for eecuring engines to hull, 
59. 

Holms' 8 screw propeller, 298, 333. 

Horses power, detiuition of, 146 ; nomi- 
nal horse power, 103-108; actual pow- 
er ascertained by the mdictator, 103, 
108 ; Admiralty rule for, 107. 

Hot water or feed pump, description of, 
49. 

Hot well, description of, 49. 



Increasing pitch of screw, 285. 

Incrustation in boilers, 188. See also 
Salt. 

India rabber valves for air pump, 228. 

Indicator, description of the, 103 ; by 
M'Naught, structure and mode of 
using, 112-115 ; Grooch's continuous 
indicator, 115. 

Injection cock, 49, 60. 

Injection cocks of marine ergines at 
ship's sides, 236. 

Injection orifice, proper area of, 162. 

Injector, Gifiard's, 347. 

Injection valve, 236, 

Inside cylinder locomotives, 255. ■ 

Iron, strength of, 25-27 ; limits of elas- 
ticity of, 27 ; proper strain to be put 
upon iron in engines and machines, 
28 ; aggravation of strain by being in- 
termittent, 29 ; increase of strain due 
to deflection, 30 ; strength of pillars 
and tubes, 32 , combination of malle- 
able and cast iron, 33. 

Iron, cast, strength of, 25-27 ; cast iron 
beams, SO ; may be strong to resist 
strains, but not strong to resist 
shocks, 32 ; should be combined with 
wrought iron to obtain maximum 
strength, 33. 

Iron, if to be case hardened, should be 
homogeneous, 386. 

Jacket of cylinder, advantages of, 91, 

218. 
Joints, rust, how to make, 385. 

Kingston's valves, 236. 



Lamb's scale preventer, 193. 
Lantern brass in stuffing boxes, 218. 
Lap and lead of the valve, meaning of, 

92. 
Large vessels have least proportionate 

rce;irJtance, 277. 
Latent heat, definition of, 71. 
Latta's steam fire engine, 362. 
Lavagrian, expansion valve bj% 100. 
Lead and lap of the valve, meaning of, 

9i 
Lead of the valve, benefits of, 157. 



Lever, 17 ; futility of plans for deriv* 
ing power from a lever, 18. 

Lifting apparatus for screw propeller, 
241. 

Limits of elasticity, 26. 

Links, main description of, 51, 62, 99, 
262. 

Link motion of direct acting screw en- 
gine, 332. 

Link motion, how to set, 394. 

Locomotive engines: general descrip- 
tion of the locomotive, 65 ; Stephen- 
son's locomotive, 66 ; Gooch's locomo- 
tive for the wide gauge, 69 ; Cramp- 
ton's locomotive for the narrow gauge, 
6^. 

Locomotives, adhesion of wheels of, 
249 ; cost and performance of, 249 ; 
framing of, 253 ; cylinders of, 254, 257 ; 
springs of, 254; outside and inside cyl- 
inders, 254 ; sinuous motion of, 255 ; 
rocking motion of, 255 ; pitching mo- 
t.on. of, 256 ; pistons, 257 ; piston 
rods, 258 ; guides, 258 ; cranked axle, 
259 ; axle bearings, 260 ; eccentrics, 
260 ; eccentric rod, 261 ; starting han- 
dle, 262; link motion, 262; valves, 
how to set, 262 ; eccentrics, how to 
readjust, 263; feed pumps, 264; con- 
nection of engine and tender, 265 ^ 
driving wheels, 266 ; wheel tires, 267. 

Locomotive engine of modern construc- 
tion, example of, 334 ; fire box, 334; 
barrel of boiler, 335 ; tubes, 335; tube 
plate, 335; framing, 335; axle guards, 
336; draw bolt, 336 ; wheels and axles, 
336 ; cylinders, 836 ; valve, 336 ; pis- 
ton, 336 ; piston rod, 336 ; guides, 336; 
connecting rod, 336: eccentrics, 337; 
link motion, 337 ; regulator, 337 ; blast 
pipe, 337; safety valve, 337; feed 
pump, 337; tendencies of improve- 
ment in locomotives, 338. 

Locomotives, management of, 403-407. 

Locomotive boilers, examples of modern 
proportions, 133. 

Locomotive boilers, details of, 199. 

Low pressure or condensing ecgine, 
definition of, 1. 

Lubrication of rubbing surfaces, 21 ; the 
friction depends mainly on the nature 
of lubricant, 21, 22; oil forced out 
of bearings, if the pressure exceeds 
800 lbs. per square inch longitudinal 
section, 28 ; water a good lubricant if 
the surfaces are large enough, 23. 

Lubrication of engine bearings, 401. 

M'Nausht's indicator, 112-115. 
Main beam, strength proper for, 168. 
Main centre, description of, 58 ; strength 

proper for, 174. 
Main links, description of, 62; Btrength 

proper for, 167. 



INDEX. 



415 



Mandrels, expanding, for tubing boilers, 
204. 

Manhole door, 36. 

Manhole of locomotives, 202. 

Marine flue boilers, proportions of, 122, 
123. See also Bjiler.^. 

Marine bollerd of modern construction, 
proper proportions of, 132. 

Marine engines. See Steam Engines, 
marine. 

Mastic cement for setting marine boil- 
ers, 180. 

Maudslay, Messrs., boilers of " Retri- 
bution" and "Great Western," by, 
122. 

Mechanical powers, 17; misconceptions 
respecting, 18. 

Mechanical power, definition of, 19 ; 
indestructible and eternal, 19; the 
sun the source of mechanical power, 
19. 

Metallic packing for pistons, 208, 220. 

Metallic packing for stuffing boxes, 219. 

Meyer, expansion valve by, 100. 

Miller, Raveahill & Co.'s modeoffix- 
mg piston rod to piston, 222. 

Modern locomotives, 334. 

Momentum, or vis viva, 8. 

Morin, experiments on friction by, 22. 

Mudholes of locomotives, 203. 

Mantz's metal, composition of, 388. 

"Niger" and "Basilisk," trials of, 291. 
"Nile," boilers of the, by Boulton and 

Watt, 126. 
Notch of eccentric should be fitted 

with brasi bush, 226. 

Oils for lubrication. 21. See Lubrica- 
tion. 

Oscillation, centre of, 12. 

Oscillating paddle engine, description 
of, 61. 

Oscillating engine, advantages of, 214 ; 
futility of objections to, 215 • details 
of cylinder, 309, 311, 321 ; framing, 
309 j condenser, 310 ; air pump, 310 ; 
trunnions, 311, 321, valve and valve 
casing, 312 ; piston, 313 , piston rod, 
314 ; air pump connecting rod and 
cross head, 315; air pump rod, 316; 
eccentric and eccentric rod, 316 , 
valve gear, 317 , valve sector, 317 , 
shaft plummer blocks, 319 , trunnion 
plunimer blocks, 319 ; feathering 
paddle wheels, 319, 320 ; packing of 
truimio is, 323. 

Oscnllatmg engines, how to erect, 391. 

Otis'8 excavator, 372. 

Outside and inside cylinder locomotives, 
254. 

Packing for stuffing box of Watt's en- 
gine, 51. 



Packing of piston of pumping engines, 
how to accomplish, 208. 

Packing of trunnions, 323. 

Paddle bolts, proper mode of forming, 
242. 

Pctddle centres, 242. 

Paddle floats, 243. 

Paddle shaft, description of, 59. 

Paddle shaft, details of, 244. 

Paddle shaft plummer blocks of oscil- 
lating engines, 319 ; 

Paddle wheels, details of, 241 ; struc- 
ture and opperation of, 278 ; slip of, 
278 ; centre of pressure of, 279 ; roll- 
ing circle, 280 , action of oblique floats, 
283 ; rule for proportioning paddle 
wheels, 283 , benefits of large floats, 
284. 

Paddle wheels, feathering, description 
of, 61 ; details of, 319. 

Paddles and screw combined, 305. 

Parallel motion, description of, 52, 59 ; 
how to lay off centres of, 390. 

Pendulum, 12 ; cause of vibrations of, 
13 ; relation of vibrations of pendu- 
lum to velocity of falling bodies, 
15; conical pendulum or governor, 
15, 16. 

Penn, Messrs., engines of "Great 
Britain," by, 64 ; direct acting screw 
engines by, 65; trunk engines by, 65. 

Performance of locomotives, 249, 250. 

Pillars, hollow, strength of, 31 ; law of 
strength varies with thickness of 
metal, 32. 

Pipe for receiving screw shaft, 239. 

Pipes of marine engines, 237. 

Piston, description^of, 46 ; how to pack 
with hemp, 208. 

Pistons, metallic packing for, 208, 220. 

Pistons for oscillating engines, 221, 313. 

Pistons, how to fit and finish, 382. 

Pistons of locomotives, 257. 

Piston rod, description of, 46, 59 ; 
strength proper for, 167, 171. 

Piston rods of locomotives, 257. 

Piston rod of oscillating engine, 313. 

Piston rods of direct acting screw en- 
gine, 327. 

Pitch of the screw, 285. 

Pitch, increasing or expanding, 285. 

Pitching motion in locomotives, 256. 

Planometers, or face plates, 383. 

Plummer blocks of shafts and trun- 
nions of oscillatinsr engines, 319. 

Plummer blocks for receiving thrust 
of screw propeller, 241, 331, 332. 

Plunfjer of feed pump, 234. 

Portable engine, Hoadley's, 351. 

Porter's patent governor, 342. 

Ports of the cylinder, area of, 157. 

Pot-lid valvos'of air pump, 227. 

Powers, mechanical, 17 ; misconcep- 
tion respecting, 18. 

Power, horses, definition of, 102 ; nom- 



416 



INDEX. 



inal and actual power, 103-108 ; pow- 
er of high pressure engines, 105. 

Power necessary for thrashing and 
grinding corn, working sugar mills, 
spinning cotton, sawing timber, 
pressing cotton, blowing furnaces, 
driving piles, and dredging earth out 
of rivers, 373-377. 

Pressing cotton, power necessary for, 
377. 

Priming, nature and causes of, 142, 143. 

Priming, if excessive, may occasion ex- 
plosion, 151. 

Propeller, screw, description of. 64. 

Proportions of screws with two, four, 
and six blades, 302, 303. 

Proving of boilers, 178. 

Prussiate of potash for case hardening, 
386. 

Pumping engines, mode of erecting, 
206 ; mode of starting, 209. 

Pumps, loss of effect in, at high speed 
and with hot water, 86, 160 ; causes 
of this loss, 164 ; remedy for, 165. 

Pumps used for mines, 211. 

Pump, air, description of, 49 ; action 
of, 51. 

Pumps, air, proper proportions of, 158 , 
single and double acting, 159. 

Pump, centrifugal, better than com- 
mon pump, 213. 

Pump, cold water, description of, 49. 

Pump, feed, description of, 49 ; action 
of, 51 ; proper dimensions of, 86 ; 
rule for proportioning, 163 ; plunger 
of, 234 ; valves of, 234 ; independent, 
344-350. 

Pump valves for mines, &c., 211, 212. 

Punching and shearing boiler plates, 
180. 

Railway wheels, bursting velocity of. 

Railway trains, resistance of, 144, 249- 
252. 

Rarefaction or exhaustion produced by 
chimneys, 139. 

*' Rattler" and " Alecto," trials of, 292. 

Registration, benefits of, 307. 

Regnault, experiments on heat by, 72, 
83. 

Regulator, a valve for regulating the 
admission of steam in locomotive.-?, 
description of, 66 : various forms of, 
205. 

Regulator, Clark's, patent steam and 
fire, 340. 

Rennie, experiments on friction "by, 21. 

Resistance, experienced by railway 
trains, 144, 250-252. 

Resistance of vessels in water, 270 ; 
mainly made up of friction, 271 ; ex- 
periments on, 273-277. 

Resistance and speed of vessela influ- 
enced by their size, 277. 



" Retribution," boilers of, by Messrs. 

Maudslay, 122. 
Riveting and caulking of land boilers, 

178. ' 

Rocking motion of locomotives, 255. 
Rolling circle of paddle wheels, 280. 
Rotatory engines, definition of, 2. 
Rotative engines, definition of, 2. 
Rust joints, how to make, 385. 



Safety valve, area of, in low pressure 
engines, 154: in locomotives, 155, 
337. 

Salinometer, or salt gauge, how to use, 
395 , how to construct, 395. 

Salt, accumulation of, prevented in 
marine boilers by blowing ofl", 5 ; 
if allowed to accumulate iu boilers 
may occasion explosion, 153 ; amount 
of, in sea water, 189. 

Salt water produces surcharged steam, 
196. 

Salting of boilers, what to do if this 
takes place, 396, 397. 

Sawing timber, power necessary for, 
376. 

Scale in marine boilers, 188. See also 
Salt. 

Scale preventer. Lamb's, 193. 

Scrap iron, unsuitable for case harden- 
ing, 386. 

Scraping tools for metal surfaces, 382. 

Screw, 17. 

Screw engine, geared oscillating, de- 
scription of, 63 ; direct acting, de- 
scription of, 65. 

Screw engine, direct acting, by Messrs. 
John Bourne & Co., 323. 

Screw engines, best forms of, 216. 

Screw frame in deadwood, 240. 

Screw propeller, description of, 63. 

Screw propeller, mode of fixing on 
shaft, 239 ; modes of receivinsr thrust, 
240 ; apparatus for lifting, 241 ; con- 
figuration of, 285 ; action of, 285 ; 
pitch of the screw, 286 , screws of 
increasing or expanding pitch, 286: 
slip of the screw, 287 , positive and 
negative slip, 287 ; screw and paddles 
compared, 288 ; test of the dynamom- 
eter, 291 •, trials of " Rattier " and 
" Alecto," and "Niger" and "Basi- 
lisk," 292 ; indicator and dynamom- 
eter power, 293 ; loss of power in 
screw vessels in head winds, 294 ; tho 
screw should be deeply immersed, 
296 .screws of the Earl ofDundonald, 
Hodgson, Griffith, Holm, and Beattie, 
298-300 ; lateral and retrogressive 
slip, 300 ; sterns of screw vessels 
should be sharp, 301 , proportions of 
screws with two, four, and six blades, 
301, 302 ; screw vessels with auxiliary 
power, 303 ; icrew and paddles com- 



INDEX. 



ill 



bined, 305 ; economy of fuel in steam 
vessels, 307 ; benetiis of registration, 
307. 
Screw propeller, Holm's conchoidal, 

333. 
Screw shaft, details of, 239. 
Screw shaft pipe at stern, 239, 331. 
Screw shaft brasses of direct acting 

screw engines, 325. 
Sea water, amount of salt in, 189. 
Sea injection cocks, 236. 
Setting of wagon boilers, 178 ; of ma- 
rine boilers, 180. 
Setting the valves of locomotives, 262. 
Shaft, paddle, details of, 244. 
Shaft of screw propeller, details of, 239. 
Shafts, strength of, 169, 170, 173. 
Shank's steam gauge, 112. 
Shocks may not be well resisted by 
iron that can well resist strains, 32 ; 
effect of inertia in resisting shocks, 
32. 
Side levers or beams, description of, 

59. 
Side lever marine engines, description 

of, 69, 60. 
Side lever engines, how to erect, 389 

-395. 
Side rods, description of, 58 ; strength 

proper for, 171. 
Silsbee, Mynderse & Co.'s steam lire 

engine, 369. 
Single acting engines, definition of, 2. 
Single acting or pumping engines, 
mode of erecting, 206; mode of 
starting, 209. 
Sinuous motion of locomotives, 255. 
Slide valve, various forms of, 91 ; long 
D and three ported valve, descrip- 
tion of, 91 ; action of the slide valve, 
92 ; lead and lap of the valve, 92 ; 
rules for determining the proportions 
of valves, 94 ; advantages of lead in 
swift moving engines, 95. 
Slide valve, equilibrium, 222-225. 
Slide valve with balance piston of 

direct acting screw engine, 326. 
Slide valve, how to finish, 383, 384. 
Slide valves of marine- engines,- how to 

set, 393. X 

Slip of paddle wheels, 278. 
Slip of the screw, 287; positive and 
negative slip, 287 ; lateral and retro- 
gressive slip, 300. 
Smoke, modes of consuming, 78-82. 
Smoke burning furnaces ; Williams's 
nrgand, 79 ; Prideaux's, 79-81 ; 
Boulrt)n and Watt's dead plate, 80 ; 
revolving grate, 80 ; Juckes's, 81 ; 
Maudslay's, 81 ; Hall's, Coupland's, 
Godson's, Robinson's, Stevens's, 
Hazeldine's, &c., 82. 
" Snake" locomotive, 334. 
Southern, experiments on friction by, 
21 ; experiments on steam by, 83. 



Specific heat, definition of, 73. 

Speed of vessels influenced by their 

size, 277. 
Spheroidal condition of water in boil- 
ers, 151. 
Springs of locomotives, 254. 
Stand pipe for low pressure boilers, 

36, 37, 119. 
Starting handle of locomotives, 262. 
Staying of boilers, 148, 149. 
Staying lube plates, mode of, 185. 
Staying fire boxes of locomotives, 

200. 
Steam, experiments on by Southern, 
French Academy, Franklin Insti- 
tute, and M. Regnault, 83. 
Steam pump^ Worthington's 344; 

Woodward' sf347. 

Steam and water, relative bulks of, 85. 

Steam, expansion of, 87 ; pressure of, 

inversely as space occupied, 88. See 

also Expansion of Steam. 

Steam engine, applications and appli. 

ances of the, 339-377. 
Steam engine : general description of 
Watt's double acting engine, 46 ; R. 
Hoe & Co.'s, 353 ; Corliss's, 354-357 ; 
Woodruft'& Beach's, 358. 
Steam engine, various forms of, for 
propelling vessels, 55-65 ; paddle en- 
gines and screw engines, 56 ; princi- 
pal varieties of paddle engines, 56 ; 
different kinds of paddle wheels, 57 ; 
the side l^ver engine, 57 ; description 
of the side lever engine, 58-60 ; oscil- 
lating paddle engine, 61 ; description 
of feathering paddle wheels, 62 ; direct 
acting screw engine, 65. 
Steam dome of locomotives, 202. 
Steam fire engine, Latta's, 362 ; Amos- 
keag, 365 ; Silsbee, Mynderse & Co.'s, 
369. 
Steam gauge, 5, 111 ; Bourdon's, 111 ; 

Shank's, 112. 
Steam jacket, benefits of 91, 218. 
Steam passages, area of, 156, 157. 
Steam room in boilers, 141, 142. 
Steam, surcharged, law of expansion 

by heat, 86. 
Steel, strength of, 26. 
Stephenson, link motion by, 98. 
Stop valves between boilers, 197. 
Straight edges, 383. 
Strains subsisting in machines, 25. 
Strain proper to be put upon iron in en- 
gines, 28. 
Strains in machines vary invei'sely as 
the velocity of the pfttlTto which the 
strain is applied, 29 ; aggravated by 
being intermittent, 29; increase of 
strain due to deflection, 30 ; effects 
of alternate strains in opposite di- 
rections, 31. 
Strength of materials, 25. 
Strength of hollow pillars, 31 ; law of 



418 



INDEX. 



strength varies "with thickneBs of 
metal, 32. 

Strength of cast iron to resist shocks 
does not vary as the strength to re- 
sist strains, 32 ; increase of strength 
by combination with cast iron, 33. 

Strength of boilers, 145 ; experiments 
on,liy Franklin Institute, 145; by 
Mr. Fairbairn, 146 ; mode of comput- 
ing, 146, 147 ; mode of staying for 
strength, 148. 

Strength of engines : cylinder, 166 •, 
trunnions, 166 ; piston rod, 167, 171 ; 
main links, 167 ; connecting rod, 167- 
171 ; studs of the beam, 168 ; gudgeons, 
168 •, working beam, 168 ; cast iron 
shaft, 169, 170 ; malleable iron shaft, 
173 ; teeth of wheels, 170 ; side rods, 
171 ; crank, 172, 173 ; crank pin, 173 ; 
cross head, 174 ; main centre, 174 ; 
gibs and cutter, 175. 

Studs, strength proper for, 168. 

Stuffing box, description of, 51. 

Stuffing boxes with metallic packing, 
219 ; with sheet brass packed behind 
with hemp, 219 ; sometimes fitted 
with a lantern brass, 213. 

Sugar mills, power necessary to work, 
375. 

Summers' experiments on the friction 
of rough surfaces, 24. 

Surcharged steam, law of expansion of, 
by heat, 85. 

Surcharged steam produaed by salt 
water, 196 ; corrosive action of, 196. 

Surfaces, how to make true, 382. 

Sweeping the tubes of boilers clean of 
Boot, 264. 

Teeth of wheels, 170. 

Telescope chimneys, 187. 

Tender of a locomotive, description of, 
68 ; attachment of, to engine, 265. 

Thrashing corn, power necessary for, 
373. 

Throttle valve, description of, 46. 

Thrust of the screw propeller, modes 
of receiving, 240. 

Thrust plummer block, 331, 332. 

Tires of locomotive w^heels, 267. 

Traction on railways, 248. 

Trunk engine by Messrs. Rennie, dis- 
advantages of, 216. 

Trunk engines by Messrs. Penn, 65. 

Trunnions of oscillating engines, des- 
cription of, 60 ; strength proper for, 
166 ; details of, 311. 

Trunnion packing, 323. 

Trunnion plummer blocks, 319. 

Tube plates, mode of staying, 185. 

Tube plates of modern locomotives, 
335. 

Tubes of modern locomotive boilers, 
835. 



Tubes of boilers, how to sweep clean of 

soot, 398. 
Tubing of boilers, 185. 
Tubing locomotive boilers, 204. 



Valve, atmospheric, 36. 

Valve casing, description of, 48. 

Valve casing should have expansion 
joint, 219. 

Valve and valve casing of oscillating 
engine, 312. 

Valve delivery, description of, 49 ; ac- 
tion of, 50. 

Valve, equilibrium slide, 222-225. 

Valve, foot, description of, 49 : action 
of, 50. 

Valve gear of Watt's engine, 49 ; ac- 
tion of, 50. 

Valve gear of oscillating engine, 317. 

Valve, gridiron, 224. 

Valve, slide. See Slide Valve. 

Valve, slide, how to finish, 383, 384. 

Valves, ball, 264 ; Belidor's might be 
used for foot and delivery valves, 
227 ; butterfly, of air pump, 227 ; 
concentric ring, for air pump bucket, 
228. 

Valves, equilibrium, 96. 

Valves, escape, for cylinders, 219. 

Valves, expansion. See Expansion 
Valves. 

Valves of feed pumps, 234. 

Valves, india rubber, for air pump, 228- 
231. 

Valves, Kingston's, 236. 

Valves of locomotives, how to set 
262. 

Valves, pot-lid, of air pump, 227. 

Vacuum, meaning of, 1 ; nature and 
uses or, 3 ; how maintained in en- 
gines, 3. 

Vacuum sometimes occurs in boilers, 
5 ; evils of a vacuum in boilers, 4. 

Vacuum, velocity with which air 
rushes into a, 4. 

Vacuum gauge, 4, 111 ; Bourdon's, 
111. 

Velocity of air entering a vacuum, 4. 

Velocity of falling bodies, 6. 

Vent of boilers, definition of, 124. 

Vessels, resistance of, 270 ; mainly 
made up of friction in good forms, 
271 ; experiments on, 273-277 ; in- 
fluence of size, 277. 

Vis viva, or mechanical power, 7. 

Waste steam pipe, 187. 

Waste water pipe, 236, 237. 

Water required for condensation, 160 ; 
pumps for supplying, 165. 

Watt's double acting engine, descrip- 
tion of, 46. 

Wedge, 17. 



INDEX. 



419 



Wheels, toothed, for screw engines, 63. 

Wheels, teeth of, 170. 

Wheels of locomotives, adhesion of, 
249. 

Wheels, driving, of locomotives, 266. 

Wheel tires, 267. 

Wheels and axles of modern locomo- 
tives, 336. 



Wood, experiments on friction by, 21. 

Wood, evaporative efficacy of, 76. 

Woodman's steam pump, 347. 

Woodruff & Beach's steam engine, 358. 

Working beam of land engine, descrip- 
tion of, 46. 

Worthington's steam pump, 344 ,» du- 
plex pump, 346. 



THE END. 




/ 



■Sfr- 



o^jJi^s 



LIBRARY OF CONGRESS 



021 225 351 



